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 $184.95   11.103%   $205.485   $205.49   $205.50   $205.50  
  Purchase #2 $161.28   13.252%   $182.6528   $182.65   $182.65   $182.70  
  Purchase #3 $218.32   4.587%   $228.3343   $228.33   $228.35   $228.30  
  Purchase #4 $65.91   13.827%   $75.0234   $75.02   $75.00   $75.00  
  Purchase #5 $61.96   9.446%   $67.8127   $67.81   $67.80   $67.80  
  Purchase #6 $99.51   7.816%   $107.2877   $107.29   $107.30   $107.30  
  Purchase #7 $18.68   9.168%   $20.3926   $20.39   $20.40   $20.40  
  7 purchase totals = $810.61       $886.9885   $886.98   $887.00   $887.00