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 $59.43   12.663%   $66.9556   $66.96   $66.95   $67.00  
  Purchase #2 $141.91   13.221%   $160.6719   $160.67   $160.65   $160.70  
  Purchase #3 $212.85   3.639%   $220.5956   $220.60   $220.60   $220.60  
  Purchase #4 $171.83   4.636%   $179.796   $179.80   $179.80   $179.80  
  Purchase #5 $233.83   10.374%   $258.0875   $258.09   $258.10   $258.10  
  Purchase #6 $48.50   7.381%   $52.0798   $52.08   $52.10   $52.10  
  Purchase #7 $125.82   10.388%   $138.8902   $138.89   $138.90   $138.90  
  7 purchase totals = $994.17       $1,077.0766   $1,077.09   $1,077.10   $1,077.20