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 $62.87   5.176%   $66.1242   $66.12   $66.10   $66.10  
  Purchase #2 $228.79   9.775%   $251.1542   $251.15   $251.15   $251.20  
  Purchase #3 $193.80   5.380%   $204.2264   $204.23   $204.25   $204.20  
  Purchase #4 $59.29   5.331%   $62.4507   $62.45   $62.45   $62.50  
  Purchase #5 $42.77   12.308%   $48.0341   $48.03   $48.05   $48.00  
  Purchase #6 $108.59   7.659%   $116.9069   $116.91   $116.90   $116.90  
  Purchase #7 $233.73   12.366%   $262.6331   $262.63   $262.65   $262.60  
  7 purchase totals = $929.84       $1,011.5296   $1,011.52   $1,011.55   $1,011.50