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 $221.93   8.722%   $241.2867   $241.29   $241.30   $241.30  
  Purchase #2 $44.91   6.310%   $47.7438   $47.74   $47.75   $47.70  
  Purchase #3 $175.52   6.806%   $187.4659   $187.47   $187.45   $187.50  
  Purchase #4 $96.77   5.870%   $102.4504   $102.45   $102.45   $102.50  
  Purchase #5 $68.35   7.760%   $73.654   $73.65   $73.65   $73.70  
  Purchase #6 $127.68   11.870%   $142.8356   $142.84   $142.85   $142.80  
  Purchase #7 $27.83   5.860%   $29.4608   $29.46   $29.45   $29.50  
  7 purchase totals = $762.99       $824.8972   $824.90   $824.90   $825.00