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 $30.94   13.688%   $35.1751   $35.18   $35.20   $35.20  
  Purchase #2 $166.66   4.230%   $173.7097   $173.71   $173.70   $173.70  
  Purchase #3 $166.62   4.815%   $174.6428   $174.64   $174.65   $174.60  
  Purchase #4 $71.89   11.607%   $80.2343   $80.23   $80.25   $80.20  
  Purchase #5 $96.72   3.228%   $99.8421   $99.84   $99.85   $99.80  
  Purchase #6 $230.83   5.321%   $243.1125   $243.11   $243.10   $243.10  
  Purchase #7 $152.68   5.451%   $161.0026   $161.00   $161.00   $161.00  
  7 purchase totals = $916.34       $967.7191   $967.71   $967.75   $967.60