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 $55.90   9.299%   $61.0981   $61.10   $61.10   $61.10  
  Purchase #2 $72.79   3.275%   $75.1739   $75.17   $75.15   $75.20  
  Purchase #3 $17.27   3.151%   $17.8142   $17.81   $17.80   $17.80  
  Purchase #4 $203.68   3.415%   $210.6357   $210.64   $210.65   $210.60  
  Purchase #5 $230.81   11.844%   $258.1471   $258.15   $258.15   $258.10  
  Purchase #6 $135.39   6.642%   $144.3826   $144.38   $144.40   $144.40  
  Purchase #7 $235.72   5.847%   $249.5025   $249.50   $249.50   $249.50  
  7 purchase totals = $951.56       $1,016.7541   $1,016.75   $1,016.75   $1,016.70