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 $207.86   11.436%   $231.6309   $231.63   $231.65   $231.60  
  Purchase #2 $11.67   8.522%   $12.6645   $12.66   $12.65   $12.70  
  Purchase #3 $145.53   5.431%   $153.4337   $153.43   $153.45   $153.40  
  Purchase #4 $31.77   5.498%   $33.5167   $33.52   $33.50   $33.50  
  Purchase #5 $72.44   5.270%   $76.2576   $76.26   $76.25   $76.30  
  Purchase #6 $201.38   4.157%   $209.7514   $209.75   $209.75   $209.80  
  Purchase #7 $242.49   5.810%   $256.5787   $256.58   $256.60   $256.60  
  7 purchase totals = $913.14       $973.8335   $973.83   $973.85   $973.90