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 $87.81   5.811%   $92.9126   $92.91   $92.90   $92.90  
  Purchase #2 $31.54   4.489%   $32.9558   $32.96   $32.95   $33.00  
  Purchase #3 $177.91   6.158%   $188.8657   $188.87   $188.85   $188.90  
  Purchase #4 $208.87   6.806%   $223.0857   $223.09   $223.10   $223.10  
  Purchase #5 $213.95   10.146%   $235.6574   $235.66   $235.65   $235.70  
  Purchase #6 $104.36   5.412%   $110.008   $110.01   $110.00   $110.00  
  Purchase #7 $161.73   10.822%   $179.2324   $179.23   $179.25   $179.20  
  7 purchase totals = $986.17       $1,062.7176   $1,062.73   $1,062.70   $1,062.80