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 $73.84   8.154%   $79.8609   $79.86   $79.85   $79.90  
  Purchase #2 $237.35   6.580%   $252.9676   $252.97   $252.95   $253.00  
  Purchase #3 $86.70   5.250%   $91.2518   $91.25   $91.25   $91.30  
  Purchase #4 $160.81   7.456%   $172.8   $172.80   $172.80   $172.80  
  Purchase #5 $123.40   7.386%   $132.5143   $132.51   $132.50   $132.50  
  Purchase #6 $234.76   5.630%   $247.977   $247.98   $248.00   $248.00  
  Purchase #7 $45.37   9.464%   $49.6638   $49.66   $49.65   $49.70  
  7 purchase totals = $962.23       $1,027.0354   $1,027.03   $1,027.00   $1,027.20