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 $86.71   5.286%   $91.2935   $91.29   $91.30   $91.30  
  Purchase #2 $207.81   10.833%   $230.3221   $230.32   $230.30   $230.30  
  Purchase #3 $145.84   6.266%   $154.9783   $154.98   $155.00   $155.00  
  Purchase #4 $107.55   7.775%   $115.912   $115.91   $115.90   $115.90  
  Purchase #5 $26.51   9.329%   $28.9831   $28.98   $29.00   $29.00  
  Purchase #6 $202.99   4.175%   $211.4648   $211.46   $211.45   $211.50  
  Purchase #7 $165.99   5.222%   $174.658   $174.66   $174.65   $174.70  
  7 purchase totals = $943.40       $1,007.6118   $1,007.60   $1,007.60   $1,007.70