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 $67.82   8.252%   $73.4165   $73.42   $73.40   $73.40  
  Purchase #2 $139.85   11.695%   $156.2055   $156.21   $156.20   $156.20  
  Purchase #3 $58.83   13.629%   $66.8479   $66.85   $66.85   $66.80  
  Purchase #4 $130.60   9.750%   $143.3335   $143.33   $143.35   $143.30  
  Purchase #5 $198.35   3.722%   $205.7326   $205.73   $205.75   $205.70  
  Purchase #6 $165.67   9.497%   $181.4037   $181.40   $181.40   $181.40  
  Purchase #7 $118.93   13.138%   $134.555   $134.56   $134.55   $134.60  
  7 purchase totals = $880.05       $961.4947   $961.50   $961.50   $961.40