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 $201.58   6.532%   $214.7472   $214.75   $214.75   $214.70  
  Purchase #2 $104.62   7.136%   $112.0857   $112.09   $112.10   $112.10  
  Purchase #3 $166.29   10.362%   $183.521   $183.52   $183.50   $183.50  
  Purchase #4 $37.45   8.609%   $40.6741   $40.67   $40.65   $40.70  
  Purchase #5 $85.51   9.122%   $93.3102   $93.31   $93.30   $93.30  
  Purchase #6 $11.35   5.124%   $11.9316   $11.93   $11.95   $11.90  
  Purchase #7 $209.44   13.190%   $237.0651   $237.07   $237.05   $237.10  
  7 purchase totals = $816.24       $893.3349   $893.34   $893.30   $893.30