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 $9.91   12.271%   $11.1261   $11.13   $11.15   $11.10  
  Purchase #2 $146.71   9.545%   $160.7135   $160.71   $160.70   $160.70  
  Purchase #3 $38.37   6.812%   $40.9838   $40.98   $41.00   $41.00  
  Purchase #4 $207.26   4.572%   $216.7359   $216.74   $216.75   $216.70  
  Purchase #5 $104.53   3.755%   $108.4551   $108.46   $108.45   $108.50  
  Purchase #6 $164.65   10.453%   $181.8609   $181.86   $181.85   $181.90  
  Purchase #7 $59.93   12.216%   $67.251   $67.25   $67.25   $67.30  
  7 purchase totals = $731.36       $787.1263   $787.13   $787.15   $787.20