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 $164.52   13.390%   $186.5492   $186.55   $186.55   $186.50  
  Purchase #2 $240.78   7.501%   $258.8409   $258.84   $258.85   $258.80  
  Purchase #3 $52.82   6.506%   $56.2565   $56.26   $56.25   $56.30  
  Purchase #4 $234.76   13.865%   $267.3095   $267.31   $267.30   $267.30  
  Purchase #5 $30.54   11.250%   $33.9758   $33.98   $34.00   $34.00  
  Purchase #6 $95.65   10.816%   $105.9955   $106.00   $106.00   $106.00  
  Purchase #7 $164.48   11.212%   $182.9215   $182.92   $182.90   $182.90  
  7 purchase totals = $983.55       $1,091.8489   $1,091.86   $1,091.85   $1,091.80