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 $46.39   12.679%   $52.2718   $52.27   $52.25   $52.30  
  Purchase #2 $83.87   8.777%   $91.2313   $91.23   $91.25   $91.20  
  Purchase #3 $160.41   8.377%   $173.8475   $173.85   $173.85   $173.80  
  Purchase #4 $168.94   6.298%   $179.5798   $179.58   $179.60   $179.60  
  Purchase #5 $170.65   7.551%   $183.5358   $183.54   $183.55   $183.50  
  Purchase #6 $234.37   5.313%   $246.8221   $246.82   $246.80   $246.80  
  Purchase #7 $127.90   6.475%   $136.1815   $136.18   $136.20   $136.20  
  7 purchase totals = $992.53       $1,063.4698   $1,063.47   $1,063.50   $1,063.40