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 $242.84   4.469%   $253.6925   $253.69   $253.70   $253.70  
  Purchase #2 $183.53   12.294%   $206.0932   $206.09   $206.10   $206.10  
  Purchase #3 $37.89   9.816%   $41.6093   $41.61   $41.60   $41.60  
  Purchase #4 $197.53   11.266%   $219.7837   $219.78   $219.80   $219.80  
  Purchase #5 $181.44   8.657%   $197.1473   $197.15   $197.15   $197.10  
  Purchase #6 $75.61   8.635%   $82.1389   $82.14   $82.15   $82.10  
  Purchase #7 $18.93   6.466%   $20.154   $20.15   $20.15   $20.20  
  7 purchase totals = $937.77       $1,020.6189   $1,020.61   $1,020.65   $1,020.60