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 $235.85   7.376%   $253.2463   $253.25   $253.25   $253.20  
  Purchase #2 $182.67   8.261%   $197.7604   $197.76   $197.75   $197.80  
  Purchase #3 $52.75   3.670%   $54.6859   $54.69   $54.70   $54.70  
  Purchase #4 $170.57   7.225%   $182.8937   $182.89   $182.90   $182.90  
  Purchase #5 $187.96   7.112%   $201.3277   $201.33   $201.35   $201.30  
  Purchase #6 $66.71   12.624%   $75.1315   $75.13   $75.15   $75.10  
  Purchase #7 $113.47   4.123%   $118.1484   $118.15   $118.15   $118.10  
  7 purchase totals = $1,009.98       $1,083.1939   $1,083.20   $1,083.25   $1,083.10