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 $73.53   4.843%   $77.0911   $77.09   $77.10   $77.10  
  Purchase #2 $179.95   3.555%   $186.3472   $186.35   $186.35   $186.30  
  Purchase #3 $109.80   8.760%   $119.4185   $119.42   $119.40   $119.40  
  Purchase #4 $195.99   5.568%   $206.9027   $206.90   $206.90   $206.90  
  Purchase #5 $180.68   12.357%   $203.0066   $203.01   $203.00   $203.00  
  Purchase #6 $213.62   8.702%   $232.2092   $232.21   $232.20   $232.20  
  Purchase #7 $105.57   11.771%   $117.9966   $118.00   $118.00   $118.00  
  7 purchase totals = $1,059.14       $1,142.9719   $1,142.98   $1,142.95   $1,142.90