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 $42.26   5.836%   $44.7263   $44.73   $44.75   $44.70  
  Purchase #2 $249.81   5.397%   $263.2922   $263.29   $263.30   $263.30  
  Purchase #3 $145.42   6.288%   $154.564   $154.56   $154.55   $154.60  
  Purchase #4 $185.67   3.550%   $192.2613   $192.26   $192.25   $192.30  
  Purchase #5 $219.73   7.390%   $235.968   $235.97   $235.95   $236.00  
  Purchase #6 $219.93   5.743%   $232.5606   $232.56   $232.55   $232.60  
  Purchase #7 $169.72   5.120%   $178.4097   $178.41   $178.40   $178.40  
  7 purchase totals = $1,232.54       $1,301.7821   $1,301.78   $1,301.75   $1,301.90