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 $63.75   7.154%   $68.3107   $68.31   $68.30   $68.30  
  Purchase #2 $74.52   5.391%   $78.5374   $78.54   $78.55   $78.50  
  Purchase #3 $221.60   11.277%   $246.5898   $246.59   $246.60   $246.60  
  Purchase #4 $205.87   9.316%   $225.0488   $225.05   $225.05   $225.00  
  Purchase #5 $190.98   7.182%   $204.6962   $204.70   $204.70   $204.70  
  Purchase #6 $148.54   3.840%   $154.2439   $154.24   $154.25   $154.20  
  Purchase #7 $83.99   3.537%   $86.9607   $86.96   $86.95   $87.00  
  7 purchase totals = $989.25       $1,064.3875   $1,064.39   $1,064.40   $1,064.30