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 $244.51   10.797%   $270.9097   $270.91   $270.90   $270.90  
  Purchase #2 $85.54   8.197%   $92.5517   $92.55   $92.55   $92.60  
  Purchase #3 $94.55   8.247%   $102.3475   $102.35   $102.35   $102.30  
  Purchase #4 $211.46   13.390%   $239.7745   $239.77   $239.75   $239.80  
  Purchase #5 $136.80   8.109%   $147.8931   $147.89   $147.90   $147.90  
  Purchase #6 $39.43   4.225%   $41.0959   $41.10   $41.10   $41.10  
  Purchase #7 $109.80   9.269%   $119.9774   $119.98   $120.00   $120.00  
  7 purchase totals = $922.09       $1,014.5498   $1,014.55   $1,014.55   $1,014.60