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 $68.65   8.320%   $74.3617   $74.36   $74.35   $74.40  
  Purchase #2 $199.65   6.751%   $213.1284   $213.13   $213.15   $213.10  
  Purchase #3 $6.35   6.584%   $6.7681   $6.77   $6.75   $6.80  
  Purchase #4 $69.37   5.444%   $73.1465   $73.15   $73.15   $73.10  
  Purchase #5 $61.91   5.552%   $65.3472   $65.35   $65.35   $65.30  
  Purchase #6 $137.28   11.488%   $153.0507   $153.05   $153.05   $153.10  
  Purchase #7 $227.67   12.406%   $255.9147   $255.91   $255.90   $255.90  
  7 purchase totals = $770.88       $841.7173   $841.72   $841.70   $841.70