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 $241.82   9.846%   $265.6296   $265.63   $265.65   $265.60  
  Purchase #2 $180.83   9.325%   $197.6924   $197.69   $197.70   $197.70  
  Purchase #3 $66.63   3.566%   $69.006   $69.01   $69.00   $69.00  
  Purchase #4 $104.82   10.339%   $115.6573   $115.66   $115.65   $115.70  
  Purchase #5 $65.39   3.431%   $67.6335   $67.63   $67.65   $67.60  
  Purchase #6 $169.61   8.741%   $184.4356   $184.44   $184.45   $184.40  
  Purchase #7 $145.28   3.306%   $150.083   $150.08   $150.10   $150.10  
  7 purchase totals = $974.38       $1,050.1374   $1,050.14   $1,050.20   $1,050.10