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 $95.96   11.758%   $107.243   $107.24   $107.25   $107.20  
  Purchase #2 $226.27   12.701%   $255.0086   $255.01   $255.00   $255.00  
  Purchase #3 $137.69   9.651%   $150.9785   $150.98   $151.00   $151.00  
  Purchase #4 $36.67   6.470%   $39.0425   $39.04   $39.05   $39.00  
  Purchase #5 $145.87   12.263%   $163.758   $163.76   $163.75   $163.80  
  Purchase #6 $170.27   3.729%   $176.6194   $176.62   $176.60   $176.60  
  Purchase #7 $146.32   7.130%   $156.7526   $156.75   $156.75   $156.80  
  7 purchase totals = $959.05       $1,049.4026   $1,049.40   $1,049.40   $1,049.40