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 $38.58   8.719%   $41.9438   $41.94   $41.95   $41.90  
  Purchase #2 $154.55   4.210%   $161.0566   $161.06   $161.05   $161.10  
  Purchase #3 $191.54   5.541%   $202.1532   $202.15   $202.15   $202.20  
  Purchase #4 $108.83   4.231%   $113.4346   $113.43   $113.45   $113.40  
  Purchase #5 $25.60   10.592%   $28.3116   $28.31   $28.30   $28.30  
  Purchase #6 $100.79   10.120%   $110.9899   $110.99   $111.00   $111.00  
  Purchase #7 $194.32   5.246%   $204.514   $204.51   $204.50   $204.50  
  7 purchase totals = $814.21       $862.4037   $862.39   $862.40   $862.40