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 $87.89   8.835%   $95.6551   $95.66   $95.65   $95.70  
  Purchase #2 $55.26   6.690%   $58.9569   $58.96   $58.95   $59.00  
  Purchase #3 $146.28   4.276%   $152.5349   $152.53   $152.55   $152.50  
  Purchase #4 $215.63   4.670%   $225.6999   $225.70   $225.70   $225.70  
  Purchase #5 $168.52   10.276%   $185.8371   $185.84   $185.85   $185.80  
  Purchase #6 $132.53   13.123%   $149.9219   $149.92   $149.90   $149.90  
  Purchase #7 $46.58   4.710%   $48.7739   $48.77   $48.75   $48.80  
  7 purchase totals = $852.69       $917.3797   $917.38   $917.35   $917.40