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 $119.80   6.461%   $127.5403   $127.54   $127.55   $127.50  
  Purchase #2 $240.35   5.201%   $252.8506   $252.85   $252.85   $252.90  
  Purchase #3 $23.35   10.693%   $25.8468   $25.85   $25.85   $25.80  
  Purchase #4 $233.43   4.345%   $243.5725   $243.57   $243.55   $243.60  
  Purchase #5 $122.60   13.539%   $139.1988   $139.20   $139.20   $139.20  
  Purchase #6 $168.96   3.445%   $174.7807   $174.78   $174.80   $174.80  
  Purchase #7 $32.55   6.559%   $34.685   $34.69   $34.70   $34.70  
  7 purchase totals = $941.04       $998.4747   $998.48   $998.50   $998.50