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 $223.62   10.693%   $247.5317   $247.53   $247.55   $247.50  
  Purchase #2 $57.28   6.416%   $60.9551   $60.96   $60.95   $61.00  
  Purchase #3 $75.68   11.169%   $84.1327   $84.13   $84.15   $84.10  
  Purchase #4 $236.71   9.673%   $259.607   $259.61   $259.60   $259.60  
  Purchase #5 $194.28   12.872%   $219.2877   $219.29   $219.30   $219.30  
  Purchase #6 $56.37   13.733%   $64.1113   $64.11   $64.10   $64.10  
  Purchase #7 $220.33   3.180%   $227.3365   $227.34   $227.35   $227.30  
  7 purchase totals = $1,064.27       $1,162.9620   $1,162.97   $1,163.00   $1,162.90