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 $210.71   12.761%   $237.5987   $237.60   $237.60   $237.60  
  Purchase #2 $87.57   9.270%   $95.6877   $95.69   $95.70   $95.70  
  Purchase #3 $49.45   3.646%   $51.2529   $51.25   $51.25   $51.30  
  Purchase #4 $56.31   12.450%   $63.3206   $63.32   $63.30   $63.30  
  Purchase #5 $101.47   11.617%   $113.2578   $113.26   $113.25   $113.30  
  Purchase #6 $131.40   13.780%   $149.5069   $149.51   $149.50   $149.50  
  Purchase #7 $32.48   3.409%   $33.5872   $33.59   $33.60   $33.60  
  7 purchase totals = $669.39       $744.2118   $744.22   $744.20   $744.30