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 $241.59   9.573%   $264.7174   $264.72   $264.70   $264.70  
  Purchase #2 $110.75   13.735%   $125.9615   $125.96   $125.95   $126.00  
  Purchase #3 $94.37   3.655%   $97.8192   $97.82   $97.80   $97.80  
  Purchase #4 $100.65   3.192%   $103.8627   $103.86   $103.85   $103.90  
  Purchase #5 $165.85   4.591%   $173.4642   $173.46   $173.45   $173.50  
  Purchase #6 $223.58   8.231%   $241.9829   $241.98   $242.00   $242.00  
  Purchase #7 $208.26   7.383%   $223.6358   $223.64   $223.65   $223.60  
  7 purchase totals = $1,145.05       $1,231.4437   $1,231.44   $1,231.40   $1,231.50