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 $174.47   10.833%   $193.3703   $193.37   $193.35   $193.40  
  Purchase #2 $87.68   12.557%   $98.69   $98.69   $98.70   $98.70  
  Purchase #3 $140.95   9.186%   $153.8977   $153.90   $153.90   $153.90  
  Purchase #4 $199.93   11.435%   $222.792   $222.79   $222.80   $222.80  
  Purchase #5 $128.85   7.341%   $138.3089   $138.31   $138.30   $138.30  
  Purchase #6 $148.60   6.302%   $157.9648   $157.96   $157.95   $158.00  
  Purchase #7 $211.30   12.226%   $237.1335   $237.13   $237.15   $237.10  
  7 purchase totals = $1,091.78       $1,202.1572   $1,202.15   $1,202.15   $1,202.20