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 $43.68   13.279%   $49.4803   $49.48   $49.50   $49.50  
  Purchase #2 $134.60   6.595%   $143.4769   $143.48   $143.50   $143.50  
  Purchase #3 $119.64   7.283%   $128.3534   $128.35   $128.35   $128.40  
  Purchase #4 $220.92   8.454%   $239.5966   $239.60   $239.60   $239.60  
  Purchase #5 $99.50   10.451%   $109.8987   $109.90   $109.90   $109.90  
  Purchase #6 $233.91   10.607%   $258.7208   $258.72   $258.70   $258.70  
  Purchase #7 $129.72   4.682%   $135.7935   $135.79   $135.80   $135.80  
  7 purchase totals = $981.97       $1,065.3202   $1,065.32   $1,065.35   $1,065.40