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 $241.54   11.500%   $269.3171   $269.32   $269.30   $269.30  
  Purchase #2 $193.98   9.750%   $212.8931   $212.89   $212.90   $212.90  
  Purchase #3 $65.26   6.847%   $69.7284   $69.73   $69.75   $69.70  
  Purchase #4 $179.66   7.445%   $193.0357   $193.04   $193.05   $193.00  
  Purchase #5 $190.44   5.431%   $200.7828   $200.78   $200.80   $200.80  
  Purchase #6 $200.91   5.506%   $211.9721   $211.97   $211.95   $212.00  
  Purchase #7 $240.49   13.608%   $273.2159   $273.22   $273.20   $273.20  
  7 purchase totals = $1,312.28       $1,430.9451   $1,430.95   $1,430.95   $1,430.90