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 $158.64   3.782%   $164.6398   $164.64   $164.65   $164.60  
  Purchase #2 $235.88   3.189%   $243.4022   $243.40   $243.40   $243.40  
  Purchase #3 $67.83   5.648%   $71.661   $71.66   $71.65   $71.70  
  Purchase #4 $108.39   7.739%   $116.7783   $116.78   $116.80   $116.80  
  Purchase #5 $160.70   5.393%   $169.3666   $169.37   $169.35   $169.40  
  Purchase #6 $229.90   12.127%   $257.78   $257.78   $257.80   $257.80  
  Purchase #7 $24.55   8.659%   $26.6758   $26.68   $26.70   $26.70  
  7 purchase totals = $985.89       $1,050.3037   $1,050.31   $1,050.35   $1,050.40