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 $56.95   8.262%   $61.6552   $61.66   $61.65   $61.70  
  Purchase #2 $125.60   7.728%   $135.3064   $135.31   $135.30   $135.30  
  Purchase #3 $141.78   6.281%   $150.6852   $150.69   $150.70   $150.70  
  Purchase #4 $89.94   5.227%   $94.6412   $94.64   $94.65   $94.60  
  Purchase #5 $212.99   6.738%   $227.3413   $227.34   $227.35   $227.30  
  Purchase #6 $37.45   12.412%   $42.0983   $42.10   $42.10   $42.10  
  Purchase #7 $198.90   6.148%   $211.1284   $211.13   $211.15   $211.10  
  7 purchase totals = $863.61       $922.8560   $922.87   $922.90   $922.80