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 $49.61   13.597%   $56.3555   $56.36   $56.35   $56.40  
  Purchase #2 $205.68   8.576%   $223.3191   $223.32   $223.30   $223.30  
  Purchase #3 $157.80   9.706%   $173.1161   $173.12   $173.10   $173.10  
  Purchase #4 $215.30   3.809%   $223.5008   $223.50   $223.50   $223.50  
  Purchase #5 $58.41   7.821%   $62.9782   $62.98   $63.00   $63.00  
  Purchase #6 $171.54   10.389%   $189.3613   $189.36   $189.35   $189.40  
  Purchase #7 $68.75   4.815%   $72.0603   $72.06   $72.05   $72.10  
  7 purchase totals = $927.09       $1,000.6913   $1,000.70   $1,000.65   $1,000.80