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 $248.29   8.199%   $268.6473   $268.65   $268.65   $268.60  
  Purchase #2 $107.78   8.434%   $116.8702   $116.87   $116.85   $116.90  
  Purchase #3 $26.62   12.776%   $30.021   $30.02   $30.00   $30.00  
  Purchase #4 $43.44   13.457%   $49.2857   $49.29   $49.30   $49.30  
  Purchase #5 $20.32   9.777%   $22.3067   $22.31   $22.30   $22.30  
  Purchase #6 $181.30   8.636%   $196.9571   $196.96   $196.95   $197.00  
  Purchase #7 $178.74   12.548%   $201.1683   $201.17   $201.15   $201.20  
  7 purchase totals = $806.49       $885.2563   $885.27   $885.20   $885.30