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 $84.56   9.327%   $92.4469   $92.45   $92.45   $92.40  
  Purchase #2 $27.95   13.373%   $31.6878   $31.69   $31.70   $31.70  
  Purchase #3 $183.46   6.672%   $195.7005   $195.70   $195.70   $195.70  
  Purchase #4 $245.54   3.751%   $254.7502   $254.75   $254.75   $254.80  
  Purchase #5 $182.80   9.607%   $200.3616   $200.36   $200.35   $200.40  
  Purchase #6 $79.41   9.223%   $86.734   $86.73   $86.75   $86.70  
  Purchase #7 $174.92   6.498%   $186.2863   $186.29   $186.30   $186.30  
  7 purchase totals = $978.64       $1,047.9673   $1,047.97   $1,048.00   $1,048.00