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 $110.66   12.623%   $124.6286   $124.63   $124.65   $124.60  
  Purchase #2 $203.90   7.211%   $218.6032   $218.60   $218.60   $218.60  
  Purchase #3 $41.47   13.615%   $47.1161   $47.12   $47.10   $47.10  
  Purchase #4 $186.80   8.634%   $202.9283   $202.93   $202.95   $202.90  
  Purchase #5 $211.67   5.287%   $222.861   $222.86   $222.85   $222.90  
  Purchase #6 $75.86   7.773%   $81.7566   $81.76   $81.75   $81.80  
  Purchase #7 $167.70   11.409%   $186.8329   $186.83   $186.85   $186.80  
  7 purchase totals = $998.06       $1,084.7267   $1,084.73   $1,084.75   $1,084.70