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 $123.36   6.815%   $131.767   $131.77   $131.75   $131.80  
  Purchase #2 $66.64   11.365%   $74.2136   $74.21   $74.20   $74.20  
  Purchase #3 $191.57   8.559%   $207.9665   $207.97   $207.95   $208.00  
  Purchase #4 $160.94   4.862%   $168.7649   $168.76   $168.75   $168.80  
  Purchase #5 $148.54   9.325%   $162.3914   $162.39   $162.40   $162.40  
  Purchase #6 $129.43   9.213%   $141.3544   $141.35   $141.35   $141.40  
  Purchase #7 $115.37   5.563%   $121.788   $121.79   $121.80   $121.80  
  7 purchase totals = $935.85       $1,008.2458   $1,008.24   $1,008.20   $1,008.40