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 $57.65   4.578%   $60.2892   $60.29   $60.30   $60.30  
  Purchase #2 $119.99   13.476%   $136.1599   $136.16   $136.15   $136.20  
  Purchase #3 $226.70   4.347%   $236.5546   $236.55   $236.55   $236.60  
  Purchase #4 $108.86   11.538%   $121.4203   $121.42   $121.40   $121.40  
  Purchase #5 $212.92   6.287%   $226.3063   $226.31   $226.30   $226.30  
  Purchase #6 $176.65   13.439%   $200.39   $200.39   $200.40   $200.40  
  Purchase #7 $136.41   6.702%   $145.5522   $145.55   $145.55   $145.60  
  7 purchase totals = $1,039.18       $1,126.6725   $1,126.67   $1,126.65   $1,126.80