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 $61.58   5.177%   $64.768   $64.77   $64.75   $64.80  
  Purchase #2 $86.96   8.204%   $94.0942   $94.09   $94.10   $94.10  
  Purchase #3 $117.90   7.787%   $127.0809   $127.08   $127.10   $127.10  
  Purchase #4 $56.80   5.169%   $59.736   $59.74   $59.75   $59.70  
  Purchase #5 $219.92   11.149%   $244.4389   $244.44   $244.45   $244.40  
  Purchase #6 $247.84   9.617%   $271.6748   $271.67   $271.65   $271.70  
  Purchase #7 $28.37   9.701%   $31.1222   $31.12   $31.10   $31.10  
  7 purchase totals = $819.37       $892.9150   $892.91   $892.90   $892.90