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 $96.83   5.124%   $101.7916   $101.79   $101.80   $101.80  
  Purchase #2 $24.36   6.147%   $25.8574   $25.86   $25.85   $25.90  
  Purchase #3 $233.36   3.318%   $241.1029   $241.10   $241.10   $241.10  
  Purchase #4 $74.45   7.547%   $80.0687   $80.07   $80.05   $80.10  
  Purchase #5 $114.33   7.475%   $122.8762   $122.88   $122.90   $122.90  
  Purchase #6 $59.97   4.265%   $62.5277   $62.53   $62.55   $62.50  
  Purchase #7 $58.59   11.278%   $65.1978   $65.20   $65.20   $65.20  
  7 purchase totals = $661.89       $699.4223   $699.43   $699.45   $699.50