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 $54.68   12.198%   $61.3499   $61.35   $61.35   $61.30  
  Purchase #2 $237.52   11.543%   $264.9369   $264.94   $264.95   $264.90  
  Purchase #3 $185.27   7.868%   $199.847   $199.85   $199.85   $199.80  
  Purchase #4 $140.78   9.127%   $153.629   $153.63   $153.65   $153.60  
  Purchase #5 $160.44   10.740%   $177.6713   $177.67   $177.65   $177.70  
  Purchase #6 $38.95   13.835%   $44.3387   $44.34   $44.35   $44.30  
  Purchase #7 $28.40   11.228%   $31.5888   $31.59   $31.60   $31.60  
  7 purchase totals = $846.04       $933.3616   $933.37   $933.40   $933.20