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 $216.58   11.427%   $241.3286   $241.33   $241.35   $241.30  
  Purchase #2 $63.33   9.798%   $69.5351   $69.54   $69.55   $69.50  
  Purchase #3 $158.69   13.493%   $180.102   $180.10   $180.10   $180.10  
  Purchase #4 $159.72   12.872%   $180.2792   $180.28   $180.30   $180.30  
  Purchase #5 $237.46   10.781%   $263.0606   $263.06   $263.05   $263.10  
  Purchase #6 $150.49   11.515%   $167.8189   $167.82   $167.80   $167.80  
  Purchase #7 $197.47   7.797%   $212.8667   $212.87   $212.85   $212.90  
  7 purchase totals = $1,183.74       $1,314.9911   $1,315.00   $1,315.00   $1,315.00