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 $232.54   7.524%   $250.0363   $250.04   $250.05   $250.00  
  Purchase #2 $138.69   5.731%   $146.6383   $146.64   $146.65   $146.60  
  Purchase #3 $20.82   8.563%   $22.6028   $22.60   $22.60   $22.60  
  Purchase #4 $7.59   6.693%   $8.098   $8.10   $8.10   $8.10  
  Purchase #5 $116.29   13.373%   $131.8415   $131.84   $131.85   $131.80  
  Purchase #6 $178.43   3.580%   $184.8178   $184.82   $184.80   $184.80  
  Purchase #7 $167.72   13.705%   $190.706   $190.71   $190.70   $190.70  
  7 purchase totals = $862.08       $934.7407   $934.75   $934.75   $934.60