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 $233.71   5.407%   $246.3467   $246.35   $246.35   $246.30  
  Purchase #2 $46.73   7.130%   $50.0618   $50.06   $50.05   $50.10  
  Purchase #3 $110.86   5.623%   $117.0937   $117.09   $117.10   $117.10  
  Purchase #4 $49.51   10.694%   $54.8046   $54.80   $54.80   $54.80  
  Purchase #5 $209.27   3.116%   $215.7909   $215.79   $215.80   $215.80  
  Purchase #6 $113.40   3.321%   $117.166   $117.17   $117.15   $117.20  
  Purchase #7 $203.55   7.614%   $219.0483   $219.05   $219.05   $219.00  
  7 purchase totals = $967.03       $1,020.3120   $1,020.31   $1,020.30   $1,020.30