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 $51.76   12.518%   $58.2393   $58.24   $58.25   $58.20  
  Purchase #2 $62.70   12.566%   $70.5789   $70.58   $70.60   $70.60  
  Purchase #3 $173.71   3.698%   $180.1338   $180.13   $180.15   $180.10  
  Purchase #4 $205.90   6.747%   $219.7921   $219.79   $219.80   $219.80  
  Purchase #5 $222.83   5.468%   $235.0143   $235.01   $235.00   $235.00  
  Purchase #6 $230.65   13.669%   $262.1775   $262.18   $262.20   $262.20  
  Purchase #7 $175.95   12.734%   $198.3555   $198.36   $198.35   $198.40  
  7 purchase totals = $1,123.50       $1,224.2914   $1,224.29   $1,224.35   $1,224.30