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 $241.79   11.294%   $269.0978   $269.10   $269.10   $269.10  
  Purchase #2 $60.79   10.264%   $67.0295   $67.03   $67.05   $67.00  
  Purchase #3 $128.65   7.107%   $137.7932   $137.79   $137.80   $137.80  
  Purchase #4 $243.93   7.360%   $261.8832   $261.88   $261.90   $261.90  
  Purchase #5 $118.79   11.432%   $132.3701   $132.37   $132.35   $132.40  
  Purchase #6 $231.54   5.414%   $244.0756   $244.08   $244.10   $244.10  
  Purchase #7 $128.65   3.130%   $132.6767   $132.68   $132.70   $132.70  
  7 purchase totals = $1,154.14       $1,244.9261   $1,244.93   $1,245.00   $1,245.00