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 $169.43   8.820%   $184.3737   $184.37   $184.35   $184.40  
  Purchase #2 $77.37   13.264%   $87.6324   $87.63   $87.65   $87.60  
  Purchase #3 $169.95   8.731%   $184.7883   $184.79   $184.80   $184.80  
  Purchase #4 $149.93   13.344%   $169.9367   $169.94   $169.95   $169.90  
  Purchase #5 $127.93   5.260%   $134.6591   $134.66   $134.65   $134.70  
  Purchase #6 $126.91   12.860%   $143.2306   $143.23   $143.25   $143.20  
  Purchase #7 $169.51   12.614%   $190.892   $190.89   $190.90   $190.90  
  7 purchase totals = $991.03       $1,095.5128   $1,095.51   $1,095.55   $1,095.50