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 $245.85   6.431%   $261.6606   $261.66   $261.65   $261.70  
  Purchase #2 $113.77   5.329%   $119.8328   $119.83   $119.85   $119.80  
  Purchase #3 $37.88   3.255%   $39.113   $39.11   $39.10   $39.10  
  Purchase #4 $240.98   9.765%   $264.5117   $264.51   $264.50   $264.50  
  Purchase #5 $69.52   9.164%   $75.8908   $75.89   $75.90   $75.90  
  Purchase #6 $160.99   3.775%   $167.0674   $167.07   $167.05   $167.10  
  Purchase #7 $87.73   7.254%   $94.0939   $94.09   $94.10   $94.10  
  7 purchase totals = $956.72       $1,022.1702   $1,022.16   $1,022.15   $1,022.20