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 $39.26   13.386%   $44.5153   $44.52   $44.50   $44.50  
  Purchase #2 $183.27   11.631%   $204.5861   $204.59   $204.60   $204.60  
  Purchase #3 $83.41   10.659%   $92.3007   $92.30   $92.30   $92.30  
  Purchase #4 $211.59   13.432%   $240.0108   $240.01   $240.00   $240.00  
  Purchase #5 $149.86   5.174%   $157.6138   $157.61   $157.60   $157.60  
  Purchase #6 $218.81   3.279%   $225.9848   $225.98   $226.00   $226.00  
  Purchase #7 $124.98   11.381%   $139.204   $139.20   $139.20   $139.20  
  7 purchase totals = $1,011.18       $1,104.2155   $1,104.21   $1,104.20   $1,104.20