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 $204.71   12.153%   $229.5884   $229.59   $229.60   $229.60  
  Purchase #2 $195.53   11.660%   $218.3288   $218.33   $218.35   $218.30  
  Purchase #3 $89.30   7.711%   $96.1859   $96.19   $96.20   $96.20  
  Purchase #4 $204.92   12.873%   $231.2994   $231.30   $231.30   $231.30  
  Purchase #5 $49.26   12.440%   $55.3879   $55.39   $55.40   $55.40  
  Purchase #6 $96.58   8.766%   $105.0462   $105.05   $105.05   $105.00  
  Purchase #7 $146.42   9.253%   $159.9682   $159.97   $159.95   $160.00  
  7 purchase totals = $986.72       $1,095.8048   $1,095.82   $1,095.85   $1,095.80