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 $168.45   6.717%   $179.7648   $179.76   $179.75   $179.80  
  Purchase #2 $247.47   3.836%   $256.9629   $256.96   $256.95   $257.00  
  Purchase #3 $120.89   4.858%   $126.7628   $126.76   $126.75   $126.80  
  Purchase #4 $45.83   12.418%   $51.5212   $51.52   $51.50   $51.50  
  Purchase #5 $223.81   9.783%   $245.7053   $245.71   $245.70   $245.70  
  Purchase #6 $49.29   7.788%   $53.1287   $53.13   $53.15   $53.10  
  Purchase #7 $115.86   3.532%   $119.9522   $119.95   $119.95   $120.00  
  7 purchase totals = $971.60       $1,033.7979   $1,033.79   $1,033.75   $1,033.90