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 $204.55   8.111%   $221.1411   $221.14   $221.15   $221.10  
  Purchase #2 $229.46   11.871%   $256.6992   $256.70   $256.70   $256.70  
  Purchase #3 $139.48   7.331%   $149.7053   $149.71   $149.70   $149.70  
  Purchase #4 $168.27   12.166%   $188.7417   $188.74   $188.75   $188.70  
  Purchase #5 $220.62   3.503%   $228.3483   $228.35   $228.35   $228.30  
  Purchase #6 $57.58   11.780%   $64.3629   $64.36   $64.35   $64.40  
  Purchase #7 $41.88   3.375%   $43.2935   $43.29   $43.30   $43.30  
  7 purchase totals = $1,061.84       $1,152.2920   $1,152.29   $1,152.30   $1,152.20