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 $205.52   8.174%   $222.3192   $222.32   $222.30   $222.30  
  Purchase #2 $67.47   7.121%   $72.2745   $72.27   $72.25   $72.30  
  Purchase #3 $173.68   11.626%   $193.872   $193.87   $193.85   $193.90  
  Purchase #4 $41.75   13.414%   $47.3503   $47.35   $47.35   $47.40  
  Purchase #5 $6.27   6.403%   $6.6715   $6.67   $6.65   $6.70  
  Purchase #6 $244.27   4.386%   $254.9837   $254.98   $255.00   $255.00  
  Purchase #7 $240.49   9.228%   $262.6824   $262.68   $262.70   $262.70  
  7 purchase totals = $979.45       $1,060.1536   $1,060.14   $1,060.10   $1,060.30