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 $242.49   8.371%   $262.7888   $262.79   $262.80   $262.80  
  Purchase #2 $75.80   7.812%   $81.7215   $81.72   $81.70   $81.70  
  Purchase #3 $225.34   7.589%   $242.4411   $242.44   $242.45   $242.40  
  Purchase #4 $244.49   11.624%   $272.9095   $272.91   $272.90   $272.90  
  Purchase #5 $145.82   7.390%   $156.5961   $156.60   $156.60   $156.60  
  Purchase #6 $57.66   9.154%   $62.9382   $62.94   $62.95   $62.90  
  Purchase #7 $174.58   5.461%   $184.1138   $184.11   $184.10   $184.10  
  7 purchase totals = $1,166.18       $1,263.5090   $1,263.51   $1,263.50   $1,263.40