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 $224.92   10.283%   $248.0485   $248.05   $248.05   $248.00  
  Purchase #2 $192.97   11.395%   $214.9589   $214.96   $214.95   $215.00  
  Purchase #3 $119.92   12.356%   $134.7373   $134.74   $134.75   $134.70  
  Purchase #4 $229.50   6.663%   $244.7916   $244.79   $244.80   $244.80  
  Purchase #5 $82.38   10.382%   $90.9327   $90.93   $90.95   $90.90  
  Purchase #6 $118.60   13.192%   $134.2457   $134.25   $134.25   $134.20  
  Purchase #7 $75.86   6.677%   $80.9252   $80.93   $80.95   $80.90  
  7 purchase totals = $1,044.15       $1,148.6399   $1,148.65   $1,148.70   $1,148.50