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 $55.86   8.479%   $60.5964   $60.60   $60.60   $60.60  
  Purchase #2 $82.79   11.122%   $91.9979   $92.00   $92.00   $92.00  
  Purchase #3 $155.92   12.840%   $175.9401   $175.94   $175.95   $175.90  
  Purchase #4 $137.49   8.334%   $148.9484   $148.95   $148.95   $148.90  
  Purchase #5 $203.79   13.191%   $230.6719   $230.67   $230.65   $230.70  
  Purchase #6 $146.36   11.511%   $163.2075   $163.21   $163.20   $163.20  
  Purchase #7 $115.47   7.741%   $124.4085   $124.41   $124.40   $124.40  
  7 purchase totals = $897.68       $995.7707   $995.78   $995.75   $995.70