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 $174.78   12.777%   $197.1116   $197.11   $197.10   $197.10  
  Purchase #2 $186.41   13.313%   $211.2268   $211.23   $211.25   $211.20  
  Purchase #3 $13.51   3.700%   $14.0099   $14.01   $14.00   $14.00  
  Purchase #4 $72.54   13.806%   $82.5549   $82.55   $82.55   $82.60  
  Purchase #5 $44.99   9.596%   $49.3072   $49.31   $49.30   $49.30  
  Purchase #6 $173.29   4.761%   $181.5403   $181.54   $181.55   $181.50  
  Purchase #7 $35.88   12.282%   $40.2868   $40.29   $40.30   $40.30  
  7 purchase totals = $701.40       $776.0375   $776.04   $776.05   $776.00