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 $56.31   6.210%   $59.8069   $59.81   $59.80   $59.80  
  Purchase #2 $193.93   4.766%   $203.1727   $203.17   $203.15   $203.20  
  Purchase #3 $165.98   6.162%   $176.2077   $176.21   $176.20   $176.20  
  Purchase #4 $249.59   11.332%   $277.8735   $277.87   $277.85   $277.90  
  Purchase #5 $207.59   6.587%   $221.264   $221.26   $221.25   $221.30  
  Purchase #6 $189.66   9.456%   $207.5942   $207.59   $207.60   $207.60  
  Purchase #7 $52.80   10.806%   $58.5056   $58.51   $58.50   $58.50  
  7 purchase totals = $1,115.86       $1,204.4246   $1,204.42   $1,204.35   $1,204.50