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 $116.85   8.530%   $126.8173   $126.82   $126.80   $126.80  
  Purchase #2 $160.81   12.652%   $181.1557   $181.16   $181.15   $181.20  
  Purchase #3 $84.50   3.245%   $87.242   $87.24   $87.25   $87.20  
  Purchase #4 $232.69   6.728%   $248.3454   $248.35   $248.35   $248.30  
  Purchase #5 $91.55   3.449%   $94.7076   $94.71   $94.70   $94.70  
  Purchase #6 $21.74   12.346%   $24.424   $24.42   $24.40   $24.40  
  Purchase #7 $175.43   13.516%   $199.1411   $199.14   $199.15   $199.10  
  7 purchase totals = $883.57       $961.8331   $961.84   $961.80   $961.70