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 $146.43   11.758%   $163.6472   $163.65   $163.65   $163.60  
  Purchase #2 $33.98   12.332%   $38.1704   $38.17   $38.15   $38.20  
  Purchase #3 $83.96   5.164%   $88.2957   $88.30   $88.30   $88.30  
  Purchase #4 $31.49   12.842%   $35.5339   $35.53   $35.55   $35.50  
  Purchase #5 $227.52   6.526%   $242.368   $242.37   $242.35   $242.40  
  Purchase #6 $96.84   11.291%   $107.7742   $107.77   $107.75   $107.80  
  Purchase #7 $74.76   10.657%   $82.7272   $82.73   $82.75   $82.70  
  7 purchase totals = $694.98       $758.5166   $758.52   $758.50   $758.50