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 $32.34   5.797%   $34.2147   $34.21   $34.20   $34.20  
  Purchase #2 $151.93   9.853%   $166.8997   $166.90   $166.90   $166.90  
  Purchase #3 $113.29   7.595%   $121.8944   $121.89   $121.90   $121.90  
  Purchase #4 $213.76   13.822%   $243.3059   $243.31   $243.30   $243.30  
  Purchase #5 $118.53   10.600%   $131.0942   $131.09   $131.10   $131.10  
  Purchase #6 $126.94   12.625%   $142.9662   $142.97   $142.95   $143.00  
  Purchase #7 $248.34   10.261%   $273.8222   $273.82   $273.80   $273.80  
  7 purchase totals = $1,005.13       $1,114.1973   $1,114.19   $1,114.15   $1,114.20