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 $88.55   9.136%   $96.6399   $96.64   $96.65   $96.60  
  Purchase #2 $190.37   11.805%   $212.8432   $212.84   $212.85   $212.80  
  Purchase #3 $247.61   9.436%   $270.9745   $270.97   $270.95   $271.00  
  Purchase #4 $215.92   4.661%   $225.984   $225.98   $226.00   $226.00  
  Purchase #5 $113.98   7.721%   $122.7804   $122.78   $122.80   $122.80  
  Purchase #6 $138.69   11.760%   $154.9999   $155.00   $155.00   $155.00  
  Purchase #7 $240.84   6.126%   $255.5939   $255.59   $255.60   $255.60  
  7 purchase totals = $1,235.96       $1,339.8158   $1,339.80   $1,339.85   $1,339.80