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 $24.63   6.771%   $26.2977   $26.30   $26.30   $26.30  
  Purchase #2 $210.40   10.181%   $231.8208   $231.82   $231.80   $231.80  
  Purchase #3 $43.79   5.689%   $46.2812   $46.28   $46.30   $46.30  
  Purchase #4 $221.87   9.435%   $242.8034   $242.80   $242.80   $242.80  
  Purchase #5 $203.50   8.432%   $220.6591   $220.66   $220.65   $220.70  
  Purchase #6 $240.59   13.140%   $272.2035   $272.20   $272.20   $272.20  
  Purchase #7 $9.29   3.303%   $9.5968   $9.60   $9.60   $9.60  
  7 purchase totals = $954.07       $1,049.6625   $1,049.66   $1,049.65   $1,049.70