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 $211.98   13.769%   $241.1675   $241.17   $241.15   $241.20  
  Purchase #2 $110.77   7.846%   $119.461   $119.46   $119.45   $119.50  
  Purchase #3 $141.29   11.783%   $157.9382   $157.94   $157.95   $157.90  
  Purchase #4 $51.64   9.406%   $56.4973   $56.50   $56.50   $56.50  
  Purchase #5 $200.85   6.163%   $213.2284   $213.23   $213.25   $213.20  
  Purchase #6 $149.51   11.727%   $167.043   $167.04   $167.05   $167.00  
  Purchase #7 $92.35   10.194%   $101.7642   $101.76   $101.75   $101.80  
  7 purchase totals = $958.39       $1,057.0996   $1,057.10   $1,057.10   $1,057.10