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 $69.57   8.432%   $75.4361   $75.44   $75.45   $75.40  
  Purchase #2 $165.89   6.594%   $176.8288   $176.83   $176.85   $176.80  
  Purchase #3 $214.49   8.788%   $233.3394   $233.34   $233.35   $233.30  
  Purchase #4 $173.73   7.119%   $186.0978   $186.10   $186.10   $186.10  
  Purchase #5 $196.66   11.416%   $219.1107   $219.11   $219.10   $219.10  
  Purchase #6 $234.66   12.151%   $263.1735   $263.17   $263.15   $263.20  
  Purchase #7 $181.29   5.242%   $190.7932   $190.79   $190.80   $190.80  
  7 purchase totals = $1,236.29       $1,344.7795   $1,344.78   $1,344.80   $1,344.70