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 $159.78   5.582%   $168.6989   $168.70   $168.70   $168.70  
  Purchase #2 $245.82   8.799%   $267.4497   $267.45   $267.45   $267.40  
  Purchase #3 $224.29   7.169%   $240.3694   $240.37   $240.35   $240.40  
  Purchase #4 $95.34   8.248%   $103.2036   $103.20   $103.20   $103.20  
  Purchase #5 $38.40   5.694%   $40.5865   $40.59   $40.60   $40.60  
  Purchase #6 $42.58   6.242%   $45.2378   $45.24   $45.25   $45.20  
  Purchase #7 $235.79   8.654%   $256.1953   $256.20   $256.20   $256.20  
  7 purchase totals = $1,042.00       $1,121.7412   $1,121.75   $1,121.75   $1,121.70