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 $211.80   10.114%   $233.2215   $233.22   $233.20   $233.20  
  Purchase #2 $203.40   7.163%   $217.9695   $217.97   $217.95   $218.00  
  Purchase #3 $130.29   7.717%   $140.3445   $140.34   $140.35   $140.30  
  Purchase #4 $25.59   10.355%   $28.2398   $28.24   $28.25   $28.20  
  Purchase #5 $240.98   11.733%   $269.2542   $269.25   $269.25   $269.30  
  Purchase #6 $112.47   5.638%   $118.8111   $118.81   $118.80   $118.80  
  Purchase #7 $61.51   7.332%   $66.0199   $66.02   $66.00   $66.00  
  7 purchase totals = $986.04       $1,073.8605   $1,073.85   $1,073.80   $1,073.80