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 $143.32   3.348%   $148.1184   $148.12   $148.10   $148.10  
  Purchase #2 $146.53   5.405%   $154.4499   $154.45   $154.45   $154.40  
  Purchase #3 $92.84   12.438%   $104.3874   $104.39   $104.40   $104.40  
  Purchase #4 $191.47   11.452%   $213.3971   $213.40   $213.40   $213.40  
  Purchase #5 $28.30   12.701%   $31.8944   $31.89   $31.90   $31.90  
  Purchase #6 $74.37   7.679%   $80.0809   $80.08   $80.10   $80.10  
  Purchase #7 $123.96   6.800%   $132.3893   $132.39   $132.40   $132.40  
  7 purchase totals = $800.79       $864.7174   $864.72   $864.75   $864.70