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 $29.51   8.574%   $32.0402   $32.04   $32.05   $32.00  
  Purchase #2 $155.93   9.424%   $170.6248   $170.62   $170.60   $170.60  
  Purchase #3 $138.80   10.757%   $153.7307   $153.73   $153.75   $153.70  
  Purchase #4 $220.29   3.313%   $227.5882   $227.59   $227.60   $227.60  
  Purchase #5 $215.88   10.155%   $237.8026   $237.80   $237.80   $237.80  
  Purchase #6 $242.74   4.750%   $254.2702   $254.27   $254.25   $254.30  
  Purchase #7 $41.43   7.311%   $44.4589   $44.46   $44.45   $44.50  
  7 purchase totals = $1,044.58       $1,120.5156   $1,120.51   $1,120.50   $1,120.50