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 $39.68   9.119%   $43.2984   $43.30   $43.30   $43.30  
  Purchase #2 $179.85   12.497%   $202.3259   $202.33   $202.35   $202.30  
  Purchase #3 $192.54   7.312%   $206.6185   $206.62   $206.60   $206.60  
  Purchase #4 $130.38   11.341%   $145.1664   $145.17   $145.15   $145.20  
  Purchase #5 $20.40   8.529%   $22.1399   $22.14   $22.15   $22.10  
  Purchase #6 $110.92   12.472%   $124.7539   $124.75   $124.75   $124.80  
  Purchase #7 $202.35   3.410%   $209.2501   $209.25   $209.25   $209.30  
  7 purchase totals = $876.12       $953.5531   $953.56   $953.55   $953.60