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 $197.71   13.711%   $224.818   $224.82   $224.80   $224.80  
  Purchase #2 $100.84   5.665%   $106.5526   $106.55   $106.55   $106.60  
  Purchase #3 $237.45   9.230%   $259.3666   $259.37   $259.35   $259.40  
  Purchase #4 $67.43   3.844%   $70.022   $70.02   $70.00   $70.00  
  Purchase #5 $117.26   7.467%   $126.0158   $126.02   $126.00   $126.00  
  Purchase #6 $169.40   12.661%   $190.8477   $190.85   $190.85   $190.80  
  Purchase #7 $76.74   10.780%   $85.0126   $85.01   $85.00   $85.00  
  7 purchase totals = $966.83       $1,062.6353   $1,062.64   $1,062.55   $1,062.60