Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $135.63   12.836%   $153.0395   $153.04   $153.05   $153.00  
  Purchase #2 $168.54   9.154%   $183.9682   $183.97   $183.95   $184.00  
  Purchase #3 $144.99   3.121%   $149.5151   $149.52   $149.50   $149.50  
  Purchase #4 $218.80   3.603%   $226.6834   $226.68   $226.70   $226.70  
  Purchase #5 $122.92   3.202%   $126.8559   $126.86   $126.85   $126.90  
  Purchase #6 $129.36   10.209%   $142.5664   $142.57   $142.55   $142.60  
  Purchase #7 $202.56   6.152%   $215.0215   $215.02   $215.00   $215.00  
  7 purchase totals = $1,122.80       $1,197.6500   $1,197.66   $1,197.60   $1,197.70