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 $64.73   9.533%   $70.9007   $70.90   $70.90   $70.90  
  Purchase #2 $114.94   4.793%   $120.4491   $120.45   $120.45   $120.40  
  Purchase #3 $116.43   12.849%   $131.3901   $131.39   $131.40   $131.40  
  Purchase #4 $30.50   12.640%   $34.3552   $34.36   $34.35   $34.40  
  Purchase #5 $65.40   5.734%   $69.15   $69.15   $69.15   $69.20  
  Purchase #6 $193.64   3.789%   $200.977   $200.98   $201.00   $201.00  
  Purchase #7 $191.32   13.717%   $217.5634   $217.56   $217.55   $217.60  
  7 purchase totals = $776.96       $844.7855   $844.79   $844.80   $844.90