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 $60.97   10.615%   $67.442   $67.44   $67.45   $67.40  
  Purchase #2 $234.37   7.470%   $251.8774   $251.88   $251.90   $251.90  
  Purchase #3 $149.68   6.277%   $159.0754   $159.08   $159.10   $159.10  
  Purchase #4 $221.57   6.247%   $235.4115   $235.41   $235.40   $235.40  
  Purchase #5 $30.29   6.808%   $32.3521   $32.35   $32.35   $32.40  
  Purchase #6 $93.31   13.606%   $106.0058   $106.01   $106.00   $106.00  
  Purchase #7 $105.50   5.745%   $111.561   $111.56   $111.55   $111.60  
  7 purchase totals = $895.69       $963.7252   $963.73   $963.75   $963.80