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 $211.83   8.507%   $229.8504   $229.85   $229.85   $229.90  
  Purchase #2 $75.67   11.599%   $84.447   $84.45   $84.45   $84.40  
  Purchase #3 $68.39   8.650%   $74.3057   $74.31   $74.30   $74.30  
  Purchase #4 $135.90   13.154%   $153.7763   $153.78   $153.80   $153.80  
  Purchase #5 $240.92   6.335%   $256.1823   $256.18   $256.20   $256.20  
  Purchase #6 $214.99   12.473%   $241.8057   $241.81   $241.80   $241.80  
  Purchase #7 $47.65   12.575%   $53.642   $53.64   $53.65   $53.60  
  7 purchase totals = $995.35       $1,094.0094   $1,094.02   $1,094.05   $1,094.00