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 $233.45   13.146%   $264.1393   $264.14   $264.15   $264.10  
  Purchase #2 $109.98   12.872%   $124.1366   $124.14   $124.15   $124.10  
  Purchase #3 $240.25   6.864%   $256.7408   $256.74   $256.75   $256.70  
  Purchase #4 $168.70   3.549%   $174.6872   $174.69   $174.70   $174.70  
  Purchase #5 $53.78   12.311%   $60.4009   $60.40   $60.40   $60.40  
  Purchase #6 $24.73   4.751%   $25.9049   $25.90   $25.90   $25.90  
  Purchase #7 $120.43   12.430%   $135.3994   $135.40   $135.40   $135.40  
  7 purchase totals = $951.32       $1,041.4091   $1,041.41   $1,041.45   $1,041.30