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 $194.79   8.801%   $211.9335   $211.93   $211.95   $211.90  
  Purchase #2 $23.78   4.521%   $24.8551   $24.86   $24.85   $24.90  
  Purchase #3 $228.41   8.538%   $247.9116   $247.91   $247.90   $247.90  
  Purchase #4 $36.40   8.545%   $39.5104   $39.51   $39.50   $39.50  
  Purchase #5 $224.72   4.656%   $235.183   $235.18   $235.20   $235.20  
  Purchase #6 $237.67   10.861%   $263.4833   $263.48   $263.50   $263.50  
  Purchase #7 $13.84   5.627%   $14.6188   $14.62   $14.60   $14.60  
  7 purchase totals = $959.61       $1,037.4957   $1,037.49   $1,037.50   $1,037.50