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 $64.63   4.598%   $67.6017   $67.60   $67.60   $67.60  
  Purchase #2 $138.66   11.798%   $155.0191   $155.02   $155.00   $155.00  
  Purchase #3 $240.28   13.480%   $272.6697   $272.67   $272.65   $272.70  
  Purchase #4 $65.41   4.337%   $68.2468   $68.25   $68.25   $68.20  
  Purchase #5 $59.75   5.158%   $62.8319   $62.83   $62.85   $62.80  
  Purchase #6 $244.32   13.530%   $277.3765   $277.38   $277.40   $277.40  
  Purchase #7 $153.83   11.147%   $170.9774   $170.98   $171.00   $171.00  
  7 purchase totals = $966.88       $1,074.7231   $1,074.73   $1,074.75   $1,074.70