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 $219.95   13.710%   $250.1051   $250.11   $250.10   $250.10  
  Purchase #2 $180.56   7.835%   $194.7069   $194.71   $194.70   $194.70  
  Purchase #3 $155.65   5.798%   $164.6746   $164.67   $164.65   $164.70  
  Purchase #4 $112.92   6.378%   $120.122   $120.12   $120.10   $120.10  
  Purchase #5 $201.65   5.587%   $212.9162   $212.92   $212.90   $212.90  
  Purchase #6 $137.66   5.596%   $145.3635   $145.36   $145.35   $145.40  
  Purchase #7 $154.69   12.158%   $173.4972   $173.50   $173.50   $173.50  
  7 purchase totals = $1,163.08       $1,261.3855   $1,261.39   $1,261.30   $1,261.40