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 $187.33   9.832%   $205.7483   $205.75   $205.75   $205.70  
  Purchase #2 $137.53   13.691%   $156.3592   $156.36   $156.35   $156.40  
  Purchase #3 $166.26   10.735%   $184.108   $184.11   $184.10   $184.10  
  Purchase #4 $233.39   9.467%   $255.485   $255.49   $255.50   $255.50  
  Purchase #5 $50.84   8.294%   $55.0567   $55.06   $55.05   $55.10  
  Purchase #6 $126.79   9.444%   $138.764   $138.76   $138.75   $138.80  
  Purchase #7 $62.87   4.463%   $65.6759   $65.68   $65.70   $65.70  
  7 purchase totals = $965.01       $1,061.1971   $1,061.21   $1,061.20   $1,061.30