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 $234.86   8.283%   $254.3135   $254.31   $254.30   $254.30  
  Purchase #2 $90.93   6.418%   $96.7659   $96.77   $96.75   $96.80  
  Purchase #3 $174.30   8.254%   $188.6867   $188.69   $188.70   $188.70  
  Purchase #4 $48.96   8.343%   $53.0447   $53.04   $53.05   $53.00  
  Purchase #5 $68.91   6.662%   $73.5008   $73.50   $73.50   $73.50  
  Purchase #6 $123.25   5.218%   $129.6812   $129.68   $129.70   $129.70  
  Purchase #7 $186.64   11.210%   $207.5623   $207.56   $207.55   $207.60  
  7 purchase totals = $927.85       $1,003.5551   $1,003.55   $1,003.55   $1,003.60