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 $193.61   5.527%   $204.3108   $204.31   $204.30   $204.30  
  Purchase #2 $38.83   11.414%   $43.2621   $43.26   $43.25   $43.30  
  Purchase #3 $25.97   5.478%   $27.3926   $27.39   $27.40   $27.40  
  Purchase #4 $131.89   8.134%   $142.6179   $142.62   $142.60   $142.60  
  Purchase #5 $126.98   9.203%   $138.666   $138.67   $138.65   $138.70  
  Purchase #6 $173.27   9.232%   $189.2663   $189.27   $189.25   $189.30  
  Purchase #7 $164.69   10.194%   $181.4785   $181.48   $181.50   $181.50  
  7 purchase totals = $855.24       $926.9942   $927.00   $926.95   $927.10