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 $132.93   13.627%   $151.0444   $151.04   $151.05   $151.00  
  Purchase #2 $210.55   10.216%   $232.0598   $232.06   $232.05   $232.10  
  Purchase #3 $150.36   13.143%   $170.1218   $170.12   $170.10   $170.10  
  Purchase #4 $90.35   12.705%   $101.829   $101.83   $101.85   $101.80  
  Purchase #5 $159.51   10.777%   $176.7004   $176.70   $176.70   $176.70  
  Purchase #6 $248.87   7.752%   $268.1624   $268.16   $268.15   $268.20  
  Purchase #7 $86.62   8.322%   $93.8285   $93.83   $93.85   $93.80  
  7 purchase totals = $1,079.19       $1,193.7463   $1,193.74   $1,193.75   $1,193.70