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 $27.43   6.867%   $29.3136   $29.31   $29.30   $29.30  
  Purchase #2 $123.66   8.636%   $134.3393   $134.34   $134.35   $134.30  
  Purchase #3 $79.85   10.184%   $87.9819   $87.98   $88.00   $88.00  
  Purchase #4 $249.54   5.484%   $263.2248   $263.22   $263.20   $263.20  
  Purchase #5 $227.97   3.432%   $235.7939   $235.79   $235.80   $235.80  
  Purchase #6 $166.30   4.654%   $174.0396   $174.04   $174.05   $174.00  
  Purchase #7 $85.94   7.405%   $92.3039   $92.30   $92.30   $92.30  
  7 purchase totals = $960.69       $1,016.9970   $1,016.98   $1,017.00   $1,016.90