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 $219.93   9.796%   $241.4743   $241.47   $241.45   $241.50  
  Purchase #2 $110.78   8.200%   $119.864   $119.86   $119.85   $119.90  
  Purchase #3 $49.89   6.594%   $53.1797   $53.18   $53.20   $53.20  
  Purchase #4 $88.93   5.827%   $94.112   $94.11   $94.10   $94.10  
  Purchase #5 $96.91   8.106%   $104.7655   $104.77   $104.75   $104.80  
  Purchase #6 $201.88   5.306%   $212.5918   $212.59   $212.60   $212.60  
  Purchase #7 $92.46   3.158%   $95.3799   $95.38   $95.40   $95.40  
  7 purchase totals = $860.78       $921.3672   $921.36   $921.35   $921.50