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 $65.93   8.723%   $71.6811   $71.68   $71.70   $71.70  
  Purchase #2 $215.38   11.368%   $239.8644   $239.86   $239.85   $239.90  
  Purchase #3 $47.99   11.521%   $53.5189   $53.52   $53.50   $53.50  
  Purchase #4 $128.27   8.344%   $138.9728   $138.97   $138.95   $139.00  
  Purchase #5 $150.30   4.829%   $157.558   $157.56   $157.55   $157.60  
  Purchase #6 $149.57   9.589%   $163.9123   $163.91   $163.90   $163.90  
  Purchase #7 $232.88   6.532%   $248.0917   $248.09   $248.10   $248.10  
  7 purchase totals = $990.32       $1,073.5992   $1,073.59   $1,073.55   $1,073.70