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 $66.65   11.817%   $74.526   $74.53   $74.55   $74.50  
  Purchase #2 $240.72   13.261%   $272.6419   $272.64   $272.65   $272.60  
  Purchase #3 $158.90   10.178%   $175.0728   $175.07   $175.05   $175.10  
  Purchase #4 $140.77   3.839%   $146.1742   $146.17   $146.15   $146.20  
  Purchase #5 $167.67   8.120%   $181.2848   $181.28   $181.30   $181.30  
  Purchase #6 $57.66   11.136%   $64.081   $64.08   $64.10   $64.10  
  Purchase #7 $160.69   8.871%   $174.9448   $174.94   $174.95   $174.90  
  7 purchase totals = $993.06       $1,088.7255   $1,088.71   $1,088.75   $1,088.70