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 $217.96   12.119%   $244.3746   $244.37   $244.35   $244.40  
  Purchase #2 $245.57   5.408%   $258.8504   $258.85   $258.85   $258.90  
  Purchase #3 $25.85   3.443%   $26.74   $26.74   $26.75   $26.70  
  Purchase #4 $203.97   6.137%   $216.4876   $216.49   $216.50   $216.50  
  Purchase #5 $21.88   4.374%   $22.837   $22.84   $22.85   $22.80  
  Purchase #6 $21.44   7.691%   $23.089   $23.09   $23.10   $23.10  
  Purchase #7 $152.52   10.556%   $168.62   $168.62   $168.60   $168.60  
  7 purchase totals = $889.19       $960.9986   $961.00   $961.00   $961.00