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 $164.77   11.765%   $184.1552   $184.16   $184.15   $184.20  
  Purchase #2 $192.97   10.858%   $213.9227   $213.92   $213.90   $213.90  
  Purchase #3 $120.53   5.347%   $126.9747   $126.97   $126.95   $127.00  
  Purchase #4 $201.60   5.588%   $212.8654   $212.87   $212.85   $212.90  
  Purchase #5 $234.85   4.538%   $245.5075   $245.51   $245.50   $245.50  
  Purchase #6 $86.55   11.698%   $96.6746   $96.67   $96.65   $96.70  
  Purchase #7 $235.46   12.766%   $265.5188   $265.52   $265.50   $265.50  
  7 purchase totals = $1,236.73       $1,345.6189   $1,345.62   $1,345.50   $1,345.70