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 $54.58   11.650%   $60.9386   $60.94   $60.95   $60.90  
  Purchase #2 $147.53   10.691%   $163.3024   $163.30   $163.30   $163.30  
  Purchase #3 $232.96   10.142%   $256.5868   $256.59   $256.60   $256.60  
  Purchase #4 $238.78   11.331%   $265.8362   $265.84   $265.85   $265.80  
  Purchase #5 $180.42   13.843%   $205.3955   $205.40   $205.40   $205.40  
  Purchase #6 $166.61   7.253%   $178.6942   $178.69   $178.70   $178.70  
  Purchase #7 $173.57   12.474%   $195.2211   $195.22   $195.20   $195.20  
  7 purchase totals = $1,194.45       $1,325.9748   $1,325.98   $1,326.00   $1,325.90