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 $81.70   11.637%   $91.2074   $91.21   $91.20   $91.20  
  Purchase #2 $98.94   8.454%   $107.3044   $107.30   $107.30   $107.30  
  Purchase #3 $113.52   5.305%   $119.5422   $119.54   $119.55   $119.50  
  Purchase #4 $65.27   12.675%   $73.543   $73.54   $73.55   $73.50  
  Purchase #5 $11.84   8.195%   $12.8103   $12.81   $12.80   $12.80  
  Purchase #6 $38.82   12.384%   $43.6275   $43.63   $43.65   $43.60  
  Purchase #7 $242.58   4.746%   $254.0928   $254.09   $254.10   $254.10  
  7 purchase totals = $652.67       $702.1276   $702.12   $702.15   $702.00