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 $23.79   3.782%   $24.6897   $24.69   $24.70   $24.70  
  Purchase #2 $33.82   8.873%   $36.8208   $36.82   $36.80   $36.80  
  Purchase #3 $122.76   9.336%   $134.2209   $134.22   $134.20   $134.20  
  Purchase #4 $24.59   4.164%   $25.6139   $25.61   $25.60   $25.60  
  Purchase #5 $81.40   4.324%   $84.9197   $84.92   $84.90   $84.90  
  Purchase #6 $169.47   8.580%   $184.0105   $184.01   $184.00   $184.00  
  Purchase #7 $200.29   4.368%   $209.0387   $209.04   $209.05   $209.00  
  7 purchase totals = $656.12       $699.3142   $699.31   $699.25   $699.20