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 $69.76   10.498%   $77.0834   $77.08   $77.10   $77.10  
  Purchase #2 $196.89   13.669%   $223.8029   $223.80   $223.80   $223.80  
  Purchase #3 $240.71   13.815%   $273.9641   $273.96   $273.95   $274.00  
  Purchase #4 $240.97   13.756%   $274.1178   $274.12   $274.10   $274.10  
  Purchase #5 $170.94   7.602%   $183.9349   $183.93   $183.95   $183.90  
  Purchase #6 $199.85   6.663%   $213.166   $213.17   $213.15   $213.20  
  Purchase #7 $55.43   3.251%   $57.232   $57.23   $57.25   $57.20  
  7 purchase totals = $1,174.55       $1,303.3011   $1,303.29   $1,303.30   $1,303.30