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 $239.55   12.790%   $270.1884   $270.19   $270.20   $270.20  
  Purchase #2 $158.66   8.781%   $172.5919   $172.59   $172.60   $172.60  
  Purchase #3 $65.77   11.454%   $73.3033   $73.30   $73.30   $73.30  
  Purchase #4 $212.55   5.687%   $224.6377   $224.64   $224.65   $224.60  
  Purchase #5 $56.35   10.156%   $62.0729   $62.07   $62.05   $62.10  
  Purchase #6 $211.99   9.578%   $232.2944   $232.29   $232.30   $232.30  
  Purchase #7 $30.89   5.786%   $32.6773   $32.68   $32.70   $32.70  
  7 purchase totals = $975.76       $1,067.7659   $1,067.76   $1,067.80   $1,067.80