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 $228.46   11.502%   $254.7375   $254.74   $254.75   $254.70  
  Purchase #2 $23.37   12.181%   $26.2167   $26.22   $26.20   $26.20  
  Purchase #3 $241.86   4.524%   $252.8017   $252.80   $252.80   $252.80  
  Purchase #4 $233.59   8.136%   $252.5949   $252.59   $252.60   $252.60  
  Purchase #5 $246.29   9.859%   $270.5717   $270.57   $270.55   $270.60  
  Purchase #6 $190.78   5.764%   $201.7766   $201.78   $201.80   $201.80  
  Purchase #7 $105.80   5.157%   $111.2561   $111.26   $111.25   $111.30  
  7 purchase totals = $1,270.15       $1,369.9552   $1,369.96   $1,369.95   $1,370.00