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 $54.94   6.679%   $58.6094   $58.61   $58.60   $58.60  
  Purchase #2 $244.85   10.131%   $269.6558   $269.66   $269.65   $269.70  
  Purchase #3 $13.32   7.632%   $14.3366   $14.34   $14.35   $14.30  
  Purchase #4 $31.69   5.456%   $33.419   $33.42   $33.40   $33.40  
  Purchase #5 $200.60   3.598%   $207.8176   $207.82   $207.80   $207.80  
  Purchase #6 $122.85   6.160%   $130.4176   $130.42   $130.40   $130.40  
  Purchase #7 $229.67   6.183%   $243.8705   $243.87   $243.85   $243.90  
  7 purchase totals = $897.92       $958.1265   $958.14   $958.05   $958.10