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 $87.46   10.403%   $96.5585   $96.56   $96.55   $96.60  
  Purchase #2 $221.84   7.582%   $238.6599   $238.66   $238.65   $238.70  
  Purchase #3 $76.42   8.602%   $82.9936   $82.99   $83.00   $83.00  
  Purchase #4 $179.28   12.604%   $201.8765   $201.88   $201.90   $201.90  
  Purchase #5 $29.92   13.461%   $33.9475   $33.95   $33.95   $33.90  
  Purchase #6 $91.66   13.860%   $104.3641   $104.36   $104.35   $104.40  
  Purchase #7 $235.87   7.719%   $254.0768   $254.08   $254.10   $254.10  
  7 purchase totals = $922.45       $1,012.4769   $1,012.48   $1,012.50   $1,012.60