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 $130.36   4.703%   $136.4908   $136.49   $136.50   $136.50  
  Purchase #2 $214.65   9.695%   $235.4603   $235.46   $235.45   $235.50  
  Purchase #3 $188.77   12.547%   $212.455   $212.46   $212.45   $212.50  
  Purchase #4 $50.65   4.111%   $52.7322   $52.73   $52.75   $52.70  
  Purchase #5 $153.65   10.585%   $169.9139   $169.91   $169.90   $169.90  
  Purchase #6 $127.51   4.475%   $133.2161   $133.22   $133.20   $133.20  
  Purchase #7 $109.46   12.698%   $123.3592   $123.36   $123.35   $123.40  
  7 purchase totals = $975.05       $1,063.6275   $1,063.63   $1,063.60   $1,063.70