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 $174.35   5.419%   $183.798   $183.80   $183.80   $183.80  
  Purchase #2 $213.68   9.536%   $234.0565   $234.06   $234.05   $234.10  
  Purchase #3 $30.43   6.263%   $32.3358   $32.34   $32.35   $32.30  
  Purchase #4 $106.28   10.345%   $117.2747   $117.27   $117.25   $117.30  
  Purchase #5 $127.82   5.655%   $135.0482   $135.05   $135.05   $135.00  
  Purchase #6 $244.79   5.300%   $257.7639   $257.76   $257.75   $257.80  
  Purchase #7 $61.31   8.699%   $66.6434   $66.64   $66.65   $66.60  
  7 purchase totals = $958.66       $1,026.9205   $1,026.92   $1,026.90   $1,026.90