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 $156.57   12.308%   $175.8406   $175.84   $175.85   $175.80  
  Purchase #2 $229.86   9.792%   $252.3679   $252.37   $252.35   $252.40  
  Purchase #3 $112.67   12.841%   $127.138   $127.14   $127.15   $127.10  
  Purchase #4 $93.51   3.710%   $96.9792   $96.98   $97.00   $97.00  
  Purchase #5 $41.89   8.468%   $45.4372   $45.44   $45.45   $45.40  
  Purchase #6 $144.70   8.576%   $157.1095   $157.11   $157.10   $157.10  
  Purchase #7 $250.41   8.428%   $271.5146   $271.51   $271.50   $271.50  
  7 purchase totals = $1,029.61       $1,126.3870   $1,126.39   $1,126.40   $1,126.30