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 $51.76   13.161%   $58.5721   $58.57   $58.55   $58.60  
  Purchase #2 $231.58   12.171%   $259.7656   $259.77   $259.75   $259.80  
  Purchase #3 $246.68   3.363%   $254.9758   $254.98   $255.00   $255.00  
  Purchase #4 $37.50   10.173%   $41.3149   $41.31   $41.30   $41.30  
  Purchase #5 $213.39   9.769%   $234.2361   $234.24   $234.25   $234.20  
  Purchase #6 $82.33   11.787%   $92.0342   $92.03   $92.05   $92.00  
  Purchase #7 $87.95   5.768%   $93.023   $93.02   $93.00   $93.00  
  7 purchase totals = $951.19       $1,033.9217   $1,033.92   $1,033.90   $1,033.90