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 $48.27   7.605%   $51.9409   $51.94   $51.95   $51.90  
  Purchase #2 $200.50   13.262%   $227.0903   $227.09   $227.10   $227.10  
  Purchase #3 $191.79   6.355%   $203.9783   $203.98   $204.00   $204.00  
  Purchase #4 $169.74   5.463%   $179.0129   $179.01   $179.00   $179.00  
  Purchase #5 $25.76   6.242%   $27.3679   $27.37   $27.35   $27.40  
  Purchase #6 $243.60   4.510%   $254.5864   $254.59   $254.60   $254.60  
  Purchase #7 $88.40   3.304%   $91.3207   $91.32   $91.30   $91.30  
  7 purchase totals = $968.06       $1,035.2974   $1,035.30   $1,035.30   $1,035.30