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 $234.51   11.708%   $261.9664   $261.97   $261.95   $262.00  
  Purchase #2 $87.59   8.322%   $94.8792   $94.88   $94.90   $94.90  
  Purchase #3 $173.37   5.355%   $182.654   $182.65   $182.65   $182.70  
  Purchase #4 $218.84   10.790%   $242.4528   $242.45   $242.45   $242.50  
  Purchase #5 $200.55   9.416%   $219.4338   $219.43   $219.45   $219.40  
  Purchase #6 $131.97   7.352%   $141.6724   $141.67   $141.65   $141.70  
  Purchase #7 $180.25   9.751%   $197.8262   $197.83   $197.85   $197.80  
  7 purchase totals = $1,227.08       $1,340.8848   $1,340.88   $1,340.90   $1,341.00