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 $59.64   8.384%   $64.6402   $64.64   $64.65   $64.60  
  Purchase #2 $230.82   7.214%   $247.4714   $247.47   $247.45   $247.50  
  Purchase #3 $180.64   12.334%   $202.9201   $202.92   $202.90   $202.90  
  Purchase #4 $16.96   13.120%   $19.1852   $19.19   $19.20   $19.20  
  Purchase #5 $122.42   4.122%   $127.4662   $127.47   $127.45   $127.50  
  Purchase #6 $11.87   4.114%   $12.3583   $12.36   $12.35   $12.40  
  Purchase #7 $187.87   12.699%   $211.7276   $211.73   $211.75   $211.70  
  7 purchase totals = $810.22       $885.7690   $885.78   $885.75   $885.80