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 $245.95   11.283%   $273.7005   $273.70   $273.70   $273.70  
  Purchase #2 $150.94   6.189%   $160.2817   $160.28   $160.30   $160.30  
  Purchase #3 $161.35   9.396%   $176.5104   $176.51   $176.50   $176.50  
  Purchase #4 $66.77   5.279%   $70.2948   $70.29   $70.30   $70.30  
  Purchase #5 $219.59   3.801%   $227.9366   $227.94   $227.95   $227.90  
  Purchase #6 $127.27   6.458%   $135.4891   $135.49   $135.50   $135.50  
  Purchase #7 $196.34   8.373%   $212.7795   $212.78   $212.80   $212.80  
  7 purchase totals = $1,168.21       $1,256.9926   $1,256.99   $1,257.05   $1,257.00