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 $188.58   12.431%   $212.0224   $212.02   $212.00   $212.00  
  Purchase #2 $166.70   8.131%   $180.2544   $180.25   $180.25   $180.30  
  Purchase #3 $187.54   8.541%   $203.5578   $203.56   $203.55   $203.60  
  Purchase #4 $195.44   3.490%   $202.2609   $202.26   $202.25   $202.30  
  Purchase #5 $55.71   5.276%   $58.6493   $58.65   $58.65   $58.60  
  Purchase #6 $250.47   6.307%   $266.2671   $266.27   $266.25   $266.30  
  Purchase #7 $173.52   4.804%   $181.8559   $181.86   $181.85   $181.90  
  7 purchase totals = $1,217.96       $1,304.8678   $1,304.87   $1,304.80   $1,305.00