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 $241.34   11.470%   $269.0217   $269.02   $269.00   $269.00  
  Purchase #2 $205.95   9.571%   $225.6615   $225.66   $225.65   $225.70  
  Purchase #3 $23.43   6.796%   $25.0223   $25.02   $25.00   $25.00  
  Purchase #4 $68.71   10.464%   $75.8998   $75.90   $75.90   $75.90  
  Purchase #5 $189.72   3.814%   $196.9559   $196.96   $196.95   $197.00  
  Purchase #6 $138.97   13.290%   $157.4391   $157.44   $157.45   $157.40  
  Purchase #7 $125.96   10.402%   $139.0624   $139.06   $139.05   $139.10  
  7 purchase totals = $994.08       $1,089.0627   $1,089.06   $1,089.00   $1,089.10