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 $164.53   11.234%   $183.0133   $183.01   $183.00   $183.00  
  Purchase #2 $29.94   7.278%   $32.119   $32.12   $32.10   $32.10  
  Purchase #3 $194.91   6.133%   $206.8638   $206.86   $206.85   $206.90  
  Purchase #4 $121.39   10.360%   $133.966   $133.97   $133.95   $134.00  
  Purchase #5 $209.34   8.559%   $227.2574   $227.26   $227.25   $227.30  
  Purchase #6 $65.25   13.483%   $74.0477   $74.05   $74.05   $74.00  
  Purchase #7 $156.78   11.178%   $174.3049   $174.30   $174.30   $174.30  
  7 purchase totals = $942.14       $1,031.5721   $1,031.57   $1,031.50   $1,031.60