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 $218.96   8.282%   $237.0943   $237.09   $237.10   $237.10  
  Purchase #2 $230.96   11.413%   $257.3195   $257.32   $257.30   $257.30  
  Purchase #3 $212.43   7.442%   $228.239   $228.24   $228.25   $228.20  
  Purchase #4 $95.86   8.791%   $104.2871   $104.29   $104.30   $104.30  
  Purchase #5 $215.50   11.672%   $240.6532   $240.65   $240.65   $240.70  
  Purchase #6 $107.70   11.872%   $120.4861   $120.49   $120.50   $120.50  
  Purchase #7 $216.79   6.171%   $230.1681   $230.17   $230.15   $230.20  
  7 purchase totals = $1,298.20       $1,418.2473   $1,418.25   $1,418.25   $1,418.30