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 $13.77   7.815%   $14.8461   $14.85   $14.85   $14.80  
  Purchase #2 $243.73   8.189%   $263.689   $263.69   $263.70   $263.70  
  Purchase #3 $32.37   13.741%   $36.818   $36.82   $36.80   $36.80  
  Purchase #4 $239.31   8.578%   $259.838   $259.84   $259.85   $259.80  
  Purchase #5 $108.87   13.497%   $123.5642   $123.56   $123.55   $123.60  
  Purchase #6 $204.27   9.655%   $223.9923   $223.99   $224.00   $224.00  
  Purchase #7 $106.79   6.338%   $113.5584   $113.56   $113.55   $113.60  
  7 purchase totals = $949.11       $1,036.3060   $1,036.31   $1,036.30   $1,036.30