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 $106.89   7.365%   $114.7624   $114.76   $114.75   $114.80  
  Purchase #2 $44.34   3.196%   $45.7571   $45.76   $45.75   $45.80  
  Purchase #3 $234.95   3.543%   $243.2743   $243.27   $243.25   $243.30  
  Purchase #4 $180.33   12.429%   $202.7432   $202.74   $202.75   $202.70  
  Purchase #5 $101.49   13.343%   $115.0318   $115.03   $115.05   $115.00  
  Purchase #6 $133.26   11.547%   $148.6475   $148.65   $148.65   $148.60  
  Purchase #7 $145.96   3.350%   $150.8497   $150.85   $150.85   $150.80  
  7 purchase totals = $947.22       $1,021.0660   $1,021.06   $1,021.05   $1,021.00