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 $92.25   11.386%   $102.7536   $102.75   $102.75   $102.80  
  Purchase #2 $101.71   4.713%   $106.5036   $106.50   $106.50   $106.50  
  Purchase #3 $158.57   5.632%   $167.5007   $167.50   $167.50   $167.50  
  Purchase #4 $90.47   13.522%   $102.7034   $102.70   $102.70   $102.70  
  Purchase #5 $245.51   11.769%   $274.4041   $274.40   $274.40   $274.40  
  Purchase #6 $150.79   5.870%   $159.6414   $159.64   $159.65   $159.60  
  Purchase #7 $174.41   10.442%   $192.6219   $192.62   $192.60   $192.60  
  7 purchase totals = $1,013.71       $1,106.1287   $1,106.11   $1,106.10   $1,106.10