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 $164.27   12.555%   $184.8941   $184.89   $184.90   $184.90  
  Purchase #2 $210.78   11.790%   $235.631   $235.63   $235.65   $235.60  
  Purchase #3 $19.94   11.513%   $22.2357   $22.24   $22.25   $22.20  
  Purchase #4 $117.69   5.523%   $124.19   $124.19   $124.20   $124.20  
  Purchase #5 $191.25   7.542%   $205.6741   $205.67   $205.65   $205.70  
  Purchase #6 $15.80   11.714%   $17.6508   $17.65   $17.65   $17.70  
  Purchase #7 $232.56   4.599%   $243.2554   $243.26   $243.25   $243.30  
  7 purchase totals = $952.29       $1,033.5311   $1,033.53   $1,033.55   $1,033.60