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 $245.37   11.655%   $273.9679   $273.97   $273.95   $274.00  
  Purchase #2 $187.36   4.434%   $195.6675   $195.67   $195.65   $195.70  
  Purchase #3 $160.68   5.749%   $169.9175   $169.92   $169.90   $169.90  
  Purchase #4 $162.91   11.367%   $181.428   $181.43   $181.45   $181.40  
  Purchase #5 $73.27   12.191%   $82.2023   $82.20   $82.20   $82.20  
  Purchase #6 $182.40   3.627%   $189.0156   $189.02   $189.00   $189.00  
  Purchase #7 $188.45   11.311%   $209.7656   $209.77   $209.75   $209.80  
  7 purchase totals = $1,200.44       $1,301.9644   $1,301.98   $1,301.90   $1,302.00