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 $5.42   11.313%   $6.0332   $6.03   $6.05   $6.00  
  Purchase #2 $184.96   11.729%   $206.654   $206.65   $206.65   $206.70  
  Purchase #3 $42.38   4.128%   $44.1294   $44.13   $44.15   $44.10  
  Purchase #4 $236.56   3.842%   $245.6486   $245.65   $245.65   $245.60  
  Purchase #5 $59.58   9.106%   $65.0054   $65.01   $65.00   $65.00  
  Purchase #6 $230.61   6.486%   $245.5674   $245.57   $245.55   $245.60  
  Purchase #7 $54.95   12.475%   $61.805   $61.81   $61.80   $61.80  
  7 purchase totals = $814.46       $874.8430   $874.85   $874.85   $874.80