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 $30.58   6.619%   $32.6041   $32.60   $32.60   $32.60  
  Purchase #2 $86.86   13.499%   $98.5852   $98.59   $98.60   $98.60  
  Purchase #3 $229.35   8.357%   $248.5168   $248.52   $248.50   $248.50  
  Purchase #4 $196.58   6.704%   $209.7587   $209.76   $209.75   $209.80  
  Purchase #5 $245.83   9.692%   $269.6558   $269.66   $269.65   $269.70  
  Purchase #6 $25.39   3.142%   $26.1878   $26.19   $26.20   $26.20  
  Purchase #7 $163.94   6.474%   $174.5535   $174.55   $174.55   $174.60  
  7 purchase totals = $978.53       $1,059.8619   $1,059.87   $1,059.85   $1,060.00