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 $167.48   13.839%   $190.6576   $190.66   $190.65   $190.70  
  Purchase #2 $250.98   11.799%   $280.5931   $280.59   $280.60   $280.60  
  Purchase #3 $154.52   13.473%   $175.3385   $175.34   $175.35   $175.30  
  Purchase #4 $64.76   3.525%   $67.0428   $67.04   $67.05   $67.00  
  Purchase #5 $117.44   5.855%   $124.3161   $124.32   $124.30   $124.30  
  Purchase #6 $15.42   5.680%   $16.2959   $16.30   $16.30   $16.30  
  Purchase #7 $235.65   12.310%   $264.6585   $264.66   $264.65   $264.70  
  7 purchase totals = $1,006.25       $1,118.9025   $1,118.91   $1,118.90   $1,118.90