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 $233.82   3.441%   $241.8657   $241.87   $241.85   $241.90  
  Purchase #2 $95.78   11.138%   $106.448   $106.45   $106.45   $106.40  
  Purchase #3 $153.92   9.366%   $168.3361   $168.34   $168.35   $168.30  
  Purchase #4 $202.61   4.322%   $211.3668   $211.37   $211.35   $211.40  
  Purchase #5 $96.66   8.488%   $104.8645   $104.86   $104.85   $104.90  
  Purchase #6 $29.77   8.710%   $32.363   $32.36   $32.35   $32.40  
  Purchase #7 $115.70   12.634%   $130.3175   $130.32   $130.30   $130.30  
  7 purchase totals = $928.26       $995.5616   $995.57   $995.50   $995.60