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 $56.97   3.562%   $58.9993   $59.00   $59.00   $59.00  
  Purchase #2 $193.44   3.718%   $200.6321   $200.63   $200.65   $200.60  
  Purchase #3 $171.44   3.224%   $176.9672   $176.97   $176.95   $177.00  
  Purchase #4 $168.31   12.520%   $189.3824   $189.38   $189.40   $189.40  
  Purchase #5 $33.82   7.872%   $36.4823   $36.48   $36.50   $36.50  
  Purchase #6 $228.54   10.222%   $251.9014   $251.90   $251.90   $251.90  
  Purchase #7 $130.82   11.317%   $145.6249   $145.62   $145.60   $145.60  
  7 purchase totals = $983.34       $1,059.9896   $1,059.98   $1,060.00   $1,060.00