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 $147.25   13.594%   $167.2672   $167.27   $167.25   $167.30  
  Purchase #2 $33.84   9.386%   $37.0162   $37.02   $37.00   $37.00  
  Purchase #3 $152.46   11.135%   $169.4364   $169.44   $169.45   $169.40  
  Purchase #4 $56.55   9.565%   $61.959   $61.96   $61.95   $62.00  
  Purchase #5 $189.42   10.279%   $208.8905   $208.89   $208.90   $208.90  
  Purchase #6 $35.78   8.437%   $38.7988   $38.80   $38.80   $38.80  
  Purchase #7 $182.41   10.718%   $201.9607   $201.96   $201.95   $202.00  
  7 purchase totals = $797.71       $885.3288   $885.34   $885.30   $885.40