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 $43.39   8.290%   $46.987   $46.99   $47.00   $47.00  
  Purchase #2 $68.32   7.862%   $73.6913   $73.69   $73.70   $73.70  
  Purchase #3 $193.30   6.426%   $205.7215   $205.72   $205.70   $205.70  
  Purchase #4 $91.49   13.119%   $103.4926   $103.49   $103.50   $103.50  
  Purchase #5 $208.54   5.235%   $219.4571   $219.46   $219.45   $219.50  
  Purchase #6 $30.61   12.290%   $34.372   $34.37   $34.35   $34.40  
  Purchase #7 $156.56   11.629%   $174.7664   $174.77   $174.75   $174.80  
  7 purchase totals = $792.21       $858.4879   $858.49   $858.45   $858.60