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 $195.45   10.556%   $216.0817   $216.08   $216.10   $216.10  
  Purchase #2 $148.31   12.285%   $166.5299   $166.53   $166.55   $166.50  
  Purchase #3 $243.63   3.819%   $252.9342   $252.93   $252.95   $252.90  
  Purchase #4 $209.58   3.391%   $216.6869   $216.69   $216.70   $216.70  
  Purchase #5 $90.64   5.827%   $95.9216   $95.92   $95.90   $95.90  
  Purchase #6 $23.27   7.862%   $25.0995   $25.10   $25.10   $25.10  
  Purchase #7 $35.46   11.525%   $39.5468   $39.55   $39.55   $39.50  
  7 purchase totals = $946.34       $1,012.8006   $1,012.80   $1,012.85   $1,012.70