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 $86.98   10.727%   $96.3103   $96.31   $96.30   $96.30  
  Purchase #2 $144.52   10.797%   $160.1238   $160.12   $160.10   $160.10  
  Purchase #3 $169.32   9.772%   $185.866   $185.87   $185.85   $185.90  
  Purchase #4 $212.71   8.421%   $230.6223   $230.62   $230.60   $230.60  
  Purchase #5 $241.79   5.310%   $254.629   $254.63   $254.65   $254.60  
  Purchase #6 $190.86   3.845%   $198.1986   $198.20   $198.20   $198.20  
  Purchase #7 $153.92   4.240%   $160.4462   $160.45   $160.45   $160.40  
  7 purchase totals = $1,200.10       $1,286.1962   $1,286.20   $1,286.15   $1,286.10