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 $60.99   13.121%   $68.9925   $68.99   $69.00   $69.00  
  Purchase #2 $150.47   12.242%   $168.8905   $168.89   $168.90   $168.90  
  Purchase #3 $96.97   6.517%   $103.2895   $103.29   $103.30   $103.30  
  Purchase #4 $174.98   12.789%   $197.3582   $197.36   $197.35   $197.40  
  Purchase #5 $72.50   5.736%   $76.6586   $76.66   $76.65   $76.70  
  Purchase #6 $181.79   8.764%   $197.7221   $197.72   $197.70   $197.70  
  Purchase #7 $87.98   12.120%   $98.6432   $98.64   $98.65   $98.60  
  7 purchase totals = $825.68       $911.5546   $911.55   $911.55   $911.60