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 $165.53   10.197%   $182.4091   $182.41   $182.40   $182.40  
  Purchase #2 $246.70   11.559%   $275.2161   $275.22   $275.20   $275.20  
  Purchase #3 $60.46   10.266%   $66.6668   $66.67   $66.65   $66.70  
  Purchase #4 $169.30   4.835%   $177.4857   $177.49   $177.50   $177.50  
  Purchase #5 $87.43   10.370%   $96.4965   $96.50   $96.50   $96.50  
  Purchase #6 $126.98   10.129%   $139.8418   $139.84   $139.85   $139.80  
  Purchase #7 $79.81   4.873%   $83.6991   $83.70   $83.70   $83.70  
  7 purchase totals = $936.21       $1,021.8151   $1,021.83   $1,021.80   $1,021.80