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 $34.84   11.472%   $38.8368   $38.84   $38.85   $38.80  
  Purchase #2 $41.38   9.229%   $45.199   $45.20   $45.20   $45.20  
  Purchase #3 $19.44   11.701%   $21.7147   $21.71   $21.70   $21.70  
  Purchase #4 $176.64   7.819%   $190.4515   $190.45   $190.45   $190.50  
  Purchase #5 $235.46   4.332%   $245.6601   $245.66   $245.65   $245.70  
  Purchase #6 $123.88   6.407%   $131.817   $131.82   $131.80   $131.80  
  Purchase #7 $126.62   7.629%   $136.2798   $136.28   $136.30   $136.30  
  7 purchase totals = $758.26       $809.9589   $809.96   $809.95   $810.00