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 $233.39   13.454%   $264.7903   $264.79   $264.80   $264.80  
  Purchase #2 $241.84   13.690%   $274.9479   $274.95   $274.95   $274.90  
  Purchase #3 $113.44   11.313%   $126.2735   $126.27   $126.25   $126.30  
  Purchase #4 $50.94   9.492%   $55.7752   $55.78   $55.80   $55.80  
  Purchase #5 $34.84   13.235%   $39.4511   $39.45   $39.45   $39.50  
  Purchase #6 $214.60   4.753%   $224.7999   $224.80   $224.80   $224.80  
  Purchase #7 $75.32   11.303%   $83.8334   $83.83   $83.85   $83.80  
  7 purchase totals = $964.37       $1,069.8713   $1,069.87   $1,069.90   $1,069.90