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 $141.76   10.267%   $156.3145   $156.31   $156.30   $156.30  
  Purchase #2 $66.60   9.655%   $73.0302   $73.03   $73.05   $73.00  
  Purchase #3 $247.98   4.526%   $259.2036   $259.20   $259.20   $259.20  
  Purchase #4 $204.35   7.748%   $220.183   $220.18   $220.20   $220.20  
  Purchase #5 $86.31   7.289%   $92.6011   $92.60   $92.60   $92.60  
  Purchase #6 $231.56   9.356%   $253.2248   $253.22   $253.20   $253.20  
  Purchase #7 $132.65   6.156%   $140.8159   $140.82   $140.80   $140.80  
  7 purchase totals = $1,111.21       $1,195.3731   $1,195.36   $1,195.35   $1,195.30