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 $204.67   12.404%   $230.0573   $230.06   $230.05   $230.10  
  Purchase #2 $228.86   7.391%   $245.775   $245.78   $245.80   $245.80  
  Purchase #3 $54.45   5.421%   $57.4017   $57.40   $57.40   $57.40  
  Purchase #4 $128.96   9.406%   $141.09   $141.09   $141.10   $141.10  
  Purchase #5 $237.62   5.822%   $251.4542   $251.45   $251.45   $251.50  
  Purchase #6 $245.38   6.420%   $261.1334   $261.13   $261.15   $261.10  
  Purchase #7 $5.43   7.450%   $5.8345   $5.83   $5.85   $5.80  
  7 purchase totals = $1,105.37       $1,192.7461   $1,192.74   $1,192.80   $1,192.80