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 $238.56   3.499%   $246.9072   $246.91   $246.90   $246.90  
  Purchase #2 $128.52   8.798%   $139.8272   $139.83   $139.85   $139.80  
  Purchase #3 $9.29   9.777%   $10.1983   $10.20   $10.20   $10.20  
  Purchase #4 $102.25   11.334%   $113.839   $113.84   $113.85   $113.80  
  Purchase #5 $205.99   11.384%   $229.4399   $229.44   $229.45   $229.40  
  Purchase #6 $224.30   4.403%   $234.1759   $234.18   $234.20   $234.20  
  Purchase #7 $64.30   4.718%   $67.3337   $67.33   $67.35   $67.30  
  7 purchase totals = $973.21       $1,041.7212   $1,041.73   $1,041.80   $1,041.60