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 $242.25   8.427%   $262.6644   $262.66   $262.65   $262.70  
  Purchase #2 $81.87   7.575%   $88.0717   $88.07   $88.05   $88.10  
  Purchase #3 $26.65   8.340%   $28.8726   $28.87   $28.85   $28.90  
  Purchase #4 $95.31   11.666%   $106.4289   $106.43   $106.45   $106.40  
  Purchase #5 $192.48   13.285%   $218.051   $218.05   $218.05   $218.10  
  Purchase #6 $108.31   8.506%   $117.5228   $117.52   $117.50   $117.50  
  Purchase #7 $53.63   4.632%   $56.1141   $56.11   $56.10   $56.10  
  7 purchase totals = $800.50       $877.7255   $877.71   $877.65   $877.80