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 $29.46   5.872%   $31.1899   $31.19   $31.20   $31.20  
  Purchase #2 $134.39   12.498%   $151.1861   $151.19   $151.20   $151.20  
  Purchase #3 $226.99   13.170%   $256.8846   $256.88   $256.90   $256.90  
  Purchase #4 $117.99   13.178%   $133.5387   $133.54   $133.55   $133.50  
  Purchase #5 $55.40   7.495%   $59.5522   $59.55   $59.55   $59.60  
  Purchase #6 $244.30   6.427%   $260.0012   $260.00   $260.00   $260.00  
  Purchase #7 $98.67   10.428%   $108.9593   $108.96   $108.95   $109.00  
  7 purchase totals = $907.20       $1,001.3120   $1,001.31   $1,001.35   $1,001.40