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 $202.58   13.804%   $230.5441   $230.54   $230.55   $230.50  
  Purchase #2 $215.30   5.304%   $226.7195   $226.72   $226.70   $226.70  
  Purchase #3 $53.84   9.614%   $59.0162   $59.02   $59.00   $59.00  
  Purchase #4 $196.58   13.845%   $223.7965   $223.80   $223.80   $223.80  
  Purchase #5 $119.47   11.239%   $132.8972   $132.90   $132.90   $132.90  
  Purchase #6 $111.72   6.556%   $119.0444   $119.04   $119.05   $119.00  
  Purchase #7 $164.89   11.656%   $184.1096   $184.11   $184.10   $184.10  
  7 purchase totals = $1,064.38       $1,176.1275   $1,176.13   $1,176.10   $1,176.00