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 $167.77   11.157%   $186.4881   $186.49   $186.50   $186.50  
  Purchase #2 $26.42   11.378%   $29.4261   $29.43   $29.45   $29.40  
  Purchase #3 $176.79   5.222%   $186.022   $186.02   $186.00   $186.00  
  Purchase #4 $147.52   13.693%   $167.7199   $167.72   $167.70   $167.70  
  Purchase #5 $167.89   11.677%   $187.4945   $187.49   $187.50   $187.50  
  Purchase #6 $72.28   4.689%   $75.6692   $75.67   $75.65   $75.70  
  Purchase #7 $191.58   11.575%   $213.7554   $213.76   $213.75   $213.80  
  7 purchase totals = $950.25       $1,046.5752   $1,046.58   $1,046.55   $1,046.60