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 $93.74   11.236%   $104.2726   $104.27   $104.25   $104.30  
  Purchase #2 $249.78   3.430%   $258.3475   $258.35   $258.35   $258.30  
  Purchase #3 $137.65   4.649%   $144.0493   $144.05   $144.05   $144.00  
  Purchase #4 $137.57   13.250%   $155.798   $155.80   $155.80   $155.80  
  Purchase #5 $205.90   13.123%   $232.9203   $232.92   $232.90   $232.90  
  Purchase #6 $222.65   11.173%   $247.5267   $247.53   $247.55   $247.50  
  Purchase #7 $170.95   5.119%   $179.7009   $179.70   $179.70   $179.70  
  7 purchase totals = $1,218.24       $1,322.6153   $1,322.62   $1,322.60   $1,322.50