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 $64.77   9.394%   $70.8545   $70.85   $70.85   $70.90  
  Purchase #2 $151.97   8.579%   $165.0075   $165.01   $165.00   $165.00  
  Purchase #3 $100.45   10.408%   $110.9048   $110.90   $110.90   $110.90  
  Purchase #4 $176.48   6.217%   $187.4518   $187.45   $187.45   $187.50  
  Purchase #5 $129.75   4.377%   $135.4292   $135.43   $135.45   $135.40  
  Purchase #6 $211.31   6.446%   $224.931   $224.93   $224.95   $224.90  
  Purchase #7 $51.32   11.297%   $57.1176   $57.12   $57.10   $57.10  
  7 purchase totals = $886.05       $951.6964   $951.69   $951.70   $951.70