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 $86.96   13.537%   $98.7318   $98.73   $98.75   $98.70  
  Purchase #2 $51.75   9.378%   $56.6031   $56.60   $56.60   $56.60  
  Purchase #3 $217.94   10.130%   $240.0173   $240.02   $240.00   $240.00  
  Purchase #4 $19.93   10.149%   $21.9527   $21.95   $21.95   $22.00  
  Purchase #5 $230.42   7.817%   $248.4319   $248.43   $248.45   $248.40  
  Purchase #6 $220.25   10.717%   $243.8542   $243.85   $243.85   $243.90  
  Purchase #7 $187.36   11.765%   $209.4029   $209.40   $209.40   $209.40  
  7 purchase totals = $1,014.61       $1,118.9939   $1,118.98   $1,119.00   $1,119.00