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 $54.83   7.498%   $58.9412   $58.94   $58.95   $58.90  
  Purchase #2 $148.53   3.638%   $153.9335   $153.93   $153.95   $153.90  
  Purchase #3 $195.49   7.205%   $209.5751   $209.58   $209.60   $209.60  
  Purchase #4 $95.78   9.658%   $105.0304   $105.03   $105.05   $105.00  
  Purchase #5 $60.58   3.803%   $62.8839   $62.88   $62.90   $62.90  
  Purchase #6 $174.98   4.419%   $182.7124   $182.71   $182.70   $182.70  
  Purchase #7 $246.74   4.739%   $258.433   $258.43   $258.45   $258.40  
  7 purchase totals = $976.93       $1,031.5095   $1,031.50   $1,031.60   $1,031.40