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 $142.70   3.280%   $147.3806   $147.38   $147.40   $147.40  
  Purchase #2 $184.65   7.767%   $198.9918   $198.99   $199.00   $199.00  
  Purchase #3 $5.43   7.836%   $5.8555   $5.86   $5.85   $5.90  
  Purchase #4 $30.69   8.805%   $33.3923   $33.39   $33.40   $33.40  
  Purchase #5 $150.78   12.777%   $170.0452   $170.05   $170.05   $170.00  
  Purchase #6 $46.39   5.295%   $48.8464   $48.85   $48.85   $48.80  
  Purchase #7 $133.96   8.185%   $144.9246   $144.92   $144.90   $144.90  
  7 purchase totals = $694.60       $749.4364   $749.44   $749.45   $749.40