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 $125.84   12.578%   $141.6682   $141.67   $141.65   $141.70  
  Purchase #2 $232.61   11.159%   $258.5669   $258.57   $258.55   $258.60  
  Purchase #3 $244.53   10.482%   $270.1616   $270.16   $270.15   $270.20  
  Purchase #4 $118.52   8.547%   $128.6499   $128.65   $128.65   $128.60  
  Purchase #5 $105.99   13.838%   $120.6569   $120.66   $120.65   $120.70  
  Purchase #6 $88.91   3.390%   $91.924   $91.92   $91.90   $91.90  
  Purchase #7 $172.94   12.323%   $194.2514   $194.25   $194.25   $194.30  
  7 purchase totals = $1,089.34       $1,205.8789   $1,205.88   $1,205.80   $1,206.00