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 $23.38   12.352%   $26.2679   $26.27   $26.25   $26.30  
  Purchase #2 $121.74   4.839%   $127.631   $127.63   $127.65   $127.60  
  Purchase #3 $158.49   11.725%   $177.073   $177.07   $177.05   $177.10  
  Purchase #4 $174.77   13.198%   $197.8361   $197.84   $197.85   $197.80  
  Purchase #5 $230.92   6.749%   $246.5048   $246.50   $246.50   $246.50  
  Purchase #6 $175.65   4.869%   $184.2024   $184.20   $184.20   $184.20  
  Purchase #7 $153.35   10.255%   $169.076   $169.08   $169.10   $169.10  
  7 purchase totals = $1,038.30       $1,128.5912   $1,128.59   $1,128.60   $1,128.60