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 $92.55   13.661%   $105.1933   $105.19   $105.20   $105.20  
  Purchase #2 $191.85   9.376%   $209.8379   $209.84   $209.85   $209.80  
  Purchase #3 $78.29   4.328%   $81.6784   $81.68   $81.70   $81.70  
  Purchase #4 $141.73   3.697%   $146.9698   $146.97   $146.95   $147.00  
  Purchase #5 $240.52   4.683%   $251.7836   $251.78   $251.80   $251.80  
  Purchase #6 $192.34   5.663%   $203.2322   $203.23   $203.25   $203.20  
  Purchase #7 $117.33   11.651%   $131.0001   $131.00   $131.00   $131.00  
  7 purchase totals = $1,054.61       $1,129.6953   $1,129.69   $1,129.75   $1,129.70