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 $36.91   12.319%   $41.4569   $41.46   $41.45   $41.50  
  Purchase #2 $242.95   6.244%   $258.1198   $258.12   $258.10   $258.10  
  Purchase #3 $147.46   6.318%   $156.7765   $156.78   $156.80   $156.80  
  Purchase #4 $202.43   3.646%   $209.8106   $209.81   $209.80   $209.80  
  Purchase #5 $59.45   13.491%   $67.4704   $67.47   $67.45   $67.50  
  Purchase #6 $94.94   11.864%   $106.2037   $106.20   $106.20   $106.20  
  Purchase #7 $196.33   3.713%   $203.6197   $203.62   $203.60   $203.60  
  7 purchase totals = $980.47       $1,043.4576   $1,043.46   $1,043.40   $1,043.50