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 $52.57   12.537%   $59.1607   $59.16   $59.15   $59.20  
  Purchase #2 $180.49   6.264%   $191.7959   $191.80   $191.80   $191.80  
  Purchase #3 $68.58   10.767%   $75.964   $75.96   $75.95   $76.00  
  Purchase #4 $55.99   9.678%   $61.4087   $61.41   $61.40   $61.40  
  Purchase #5 $243.38   5.184%   $255.9968   $256.00   $256.00   $256.00  
  Purchase #6 $150.46   6.467%   $160.1902   $160.19   $160.20   $160.20  
  Purchase #7 $187.41   12.453%   $210.7482   $210.75   $210.75   $210.70  
  7 purchase totals = $938.88       $1,015.2645   $1,015.27   $1,015.25   $1,015.30