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 $116.95   8.539%   $126.9364   $126.94   $126.95   $126.90  
  Purchase #2 $103.28   10.297%   $113.9147   $113.91   $113.90   $113.90  
  Purchase #3 $174.57   9.620%   $191.3636   $191.36   $191.35   $191.40  
  Purchase #4 $168.26   3.765%   $174.595   $174.60   $174.60   $174.60  
  Purchase #5 $137.65   7.529%   $148.0137   $148.01   $148.00   $148.00  
  Purchase #6 $44.53   3.106%   $45.9131   $45.91   $45.90   $45.90  
  Purchase #7 $14.87   11.213%   $16.5374   $16.54   $16.55   $16.50  
  7 purchase totals = $760.11       $817.2739   $817.27   $817.25   $817.20