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 $92.49   11.348%   $102.9858   $102.99   $103.00   $103.00  
  Purchase #2 $226.87   4.480%   $237.0338   $237.03   $237.05   $237.00  
  Purchase #3 $218.80   4.840%   $229.3899   $229.39   $229.40   $229.40  
  Purchase #4 $190.27   11.433%   $212.0236   $212.02   $212.00   $212.00  
  Purchase #5 $225.90   3.426%   $233.6393   $233.64   $233.65   $233.60  
  Purchase #6 $199.52   10.770%   $221.0083   $221.01   $221.00   $221.00  
  Purchase #7 $85.48   4.371%   $89.2163   $89.22   $89.20   $89.20  
  7 purchase totals = $1,239.33       $1,325.2970   $1,325.30   $1,325.30   $1,325.20