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 $132.75   12.419%   $149.2362   $149.24   $149.25   $149.20  
  Purchase #2 $61.34   8.594%   $66.6116   $66.61   $66.60   $66.60  
  Purchase #3 $85.51   6.568%   $91.1263   $91.13   $91.15   $91.10  
  Purchase #4 $66.87   12.821%   $75.4434   $75.44   $75.45   $75.40  
  Purchase #5 $202.32   3.791%   $209.99   $209.99   $210.00   $210.00  
  Purchase #6 $201.59   12.668%   $227.1274   $227.13   $227.15   $227.10  
  Purchase #7 $31.71   6.260%   $33.695   $33.70   $33.70   $33.70  
  7 purchase totals = $782.09       $853.2299   $853.24   $853.30   $853.10