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 $188.62   3.275%   $194.7973   $194.80   $194.80   $194.80  
  Purchase #2 $246.56   4.498%   $257.6503   $257.65   $257.65   $257.70  
  Purchase #3 $118.72   8.423%   $128.7198   $128.72   $128.70   $128.70  
  Purchase #4 $240.27   10.720%   $266.0269   $266.03   $266.05   $266.00  
  Purchase #5 $44.70   5.761%   $47.2752   $47.28   $47.30   $47.30  
  Purchase #6 $148.47   9.787%   $163.0008   $163.00   $163.00   $163.00  
  Purchase #7 $88.67   12.472%   $99.7289   $99.73   $99.75   $99.70  
  7 purchase totals = $1,076.01       $1,157.1992   $1,157.21   $1,157.25   $1,157.20