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 $181.54   11.797%   $202.9563   $202.96   $202.95   $203.00  
  Purchase #2 $182.37   11.814%   $203.9152   $203.92   $203.90   $203.90  
  Purchase #3 $24.49   5.457%   $25.8264   $25.83   $25.85   $25.80  
  Purchase #4 $106.26   6.667%   $113.3444   $113.34   $113.35   $113.30  
  Purchase #5 $102.58   4.806%   $107.51   $107.51   $107.50   $107.50  
  Purchase #6 $49.91   12.606%   $56.2017   $56.20   $56.20   $56.20  
  Purchase #7 $205.79   5.268%   $216.631   $216.63   $216.65   $216.60  
  7 purchase totals = $852.94       $926.3850   $926.39   $926.40   $926.30