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 $154.34   13.126%   $174.5987   $174.60   $174.60   $174.60  
  Purchase #2 $119.58   12.479%   $134.5024   $134.50   $134.50   $134.50  
  Purchase #3 $208.88   12.629%   $235.2595   $235.26   $235.25   $235.30  
  Purchase #4 $143.92   10.559%   $159.1165   $159.12   $159.10   $159.10  
  Purchase #5 $8.94   3.205%   $9.2265   $9.23   $9.25   $9.20  
  Purchase #6 $43.36   13.813%   $49.3493   $49.35   $49.35   $49.30  
  Purchase #7 $39.72   11.477%   $44.2787   $44.28   $44.30   $44.30  
  7 purchase totals = $718.74       $806.3316   $806.34   $806.35   $806.30