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 $64.37   13.418%   $73.0072   $73.01   $73.00   $73.00  
  Purchase #2 $60.46   7.629%   $65.0725   $65.07   $65.05   $65.10  
  Purchase #3 $72.84   13.804%   $82.8948   $82.89   $82.90   $82.90  
  Purchase #4 $58.31   7.558%   $62.7171   $62.72   $62.70   $62.70  
  Purchase #5 $10.42   8.249%   $11.2795   $11.28   $11.30   $11.30  
  Purchase #6 $169.28   10.835%   $187.6215   $187.62   $187.60   $187.60  
  Purchase #7 $190.74   13.320%   $216.1466   $216.15   $216.15   $216.10  
  7 purchase totals = $626.42       $698.7392   $698.74   $698.70   $698.70