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 $56.41   9.742%   $61.9055   $61.91   $61.90   $61.90  
  Purchase #2 $89.55   11.128%   $99.5151   $99.52   $99.50   $99.50  
  Purchase #3 $97.63   8.629%   $106.0545   $106.05   $106.05   $106.10  
  Purchase #4 $223.86   10.116%   $246.5057   $246.51   $246.50   $246.50  
  Purchase #5 $163.32   8.581%   $177.3345   $177.33   $177.35   $177.30  
  Purchase #6 $184.84   13.452%   $209.7047   $209.70   $209.70   $209.70  
  Purchase #7 $202.56   3.323%   $209.2911   $209.29   $209.30   $209.30  
  7 purchase totals = $1,018.17       $1,110.3111   $1,110.31   $1,110.30   $1,110.30