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 $203.71   10.574%   $225.2503   $225.25   $225.25   $225.30  
  Purchase #2 $57.36   5.288%   $60.3932   $60.39   $60.40   $60.40  
  Purchase #3 $232.94   13.133%   $263.532   $263.53   $263.55   $263.50  
  Purchase #4 $14.35   4.419%   $14.9841   $14.98   $15.00   $15.00  
  Purchase #5 $109.52   9.852%   $120.3099   $120.31   $120.30   $120.30  
  Purchase #6 $138.38   9.679%   $151.7738   $151.77   $151.75   $151.80  
  Purchase #7 $141.65   7.583%   $152.3913   $152.39   $152.40   $152.40  
  7 purchase totals = $897.91       $988.6346   $988.62   $988.65   $988.70