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 $202.93   7.323%   $217.7906   $217.79   $217.80   $217.80  
  Purchase #2 $151.72   10.523%   $167.6855   $167.69   $167.70   $167.70  
  Purchase #3 $27.99   8.559%   $30.3857   $30.39   $30.40   $30.40  
  Purchase #4 $148.50   10.831%   $164.584   $164.58   $164.60   $164.60  
  Purchase #5 $180.85   4.696%   $189.3427   $189.34   $189.35   $189.30  
  Purchase #6 $201.41   11.164%   $223.8954   $223.90   $223.90   $223.90  
  Purchase #7 $18.47   11.777%   $20.6452   $20.65   $20.65   $20.60  
  7 purchase totals = $931.87       $1,014.3291   $1,014.34   $1,014.40   $1,014.30