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 $81.33   6.766%   $86.8328   $86.83   $86.85   $86.80  
  Purchase #2 $198.42   4.503%   $207.3549   $207.35   $207.35   $207.40  
  Purchase #3 $122.25   5.254%   $128.673   $128.67   $128.65   $128.70  
  Purchase #4 $102.87   13.164%   $116.4118   $116.41   $116.40   $116.40  
  Purchase #5 $238.26   7.109%   $255.1979   $255.20   $255.20   $255.20  
  Purchase #6 $223.90   13.346%   $253.7817   $253.78   $253.80   $253.80  
  Purchase #7 $82.33   5.712%   $87.0327   $87.03   $87.05   $87.00  
  7 purchase totals = $1,049.36       $1,135.2848   $1,135.27   $1,135.30   $1,135.30