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 $226.65   7.661%   $244.0137   $244.01   $244.00   $244.00  
  Purchase #2 $70.36   3.707%   $72.9682   $72.97   $72.95   $73.00  
  Purchase #3 $249.67   13.669%   $283.7974   $283.80   $283.80   $283.80  
  Purchase #4 $215.76   8.265%   $233.5926   $233.59   $233.60   $233.60  
  Purchase #5 $202.69   4.119%   $211.0388   $211.04   $211.05   $211.00  
  Purchase #6 $19.59   5.404%   $20.6486   $20.65   $20.65   $20.60  
  Purchase #7 $185.62   9.246%   $202.7824   $202.78   $202.80   $202.80  
  7 purchase totals = $1,170.34       $1,268.8417   $1,268.84   $1,268.85   $1,268.80