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 $246.40   6.701%   $262.9113   $262.91   $262.90   $262.90  
  Purchase #2 $106.52   5.639%   $112.5267   $112.53   $112.55   $112.50  
  Purchase #3 $205.96   6.466%   $219.2774   $219.28   $219.30   $219.30  
  Purchase #4 $44.45   9.214%   $48.5456   $48.55   $48.55   $48.50  
  Purchase #5 $107.97   10.269%   $119.0574   $119.06   $119.05   $119.10  
  Purchase #6 $209.74   5.482%   $221.2379   $221.24   $221.25   $221.20  
  Purchase #7 $34.51   4.158%   $35.9449   $35.94   $35.95   $35.90  
  7 purchase totals = $955.55       $1,019.5012   $1,019.51   $1,019.55   $1,019.40