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 $222.84   12.481%   $250.6527   $250.65   $250.65   $250.70  
  Purchase #2 $126.26   9.460%   $138.2042   $138.20   $138.20   $138.20  
  Purchase #3 $169.85   9.112%   $185.3267   $185.33   $185.35   $185.30  
  Purchase #4 $50.42   9.182%   $55.0496   $55.05   $55.05   $55.00  
  Purchase #5 $116.77   5.587%   $123.2939   $123.29   $123.30   $123.30  
  Purchase #6 $97.64   7.355%   $104.8214   $104.82   $104.80   $104.80  
  Purchase #7 $183.32   5.397%   $193.2138   $193.21   $193.20   $193.20  
  7 purchase totals = $967.10       $1,050.5623   $1,050.55   $1,050.55   $1,050.50