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 $69.86   9.708%   $76.642   $76.64   $76.65   $76.60  
  Purchase #2 $96.59   11.794%   $107.9818   $107.98   $108.00   $108.00  
  Purchase #3 $70.74   6.751%   $75.5157   $75.52   $75.50   $75.50  
  Purchase #4 $131.99   6.265%   $140.2592   $140.26   $140.25   $140.30  
  Purchase #5 $133.36   10.677%   $147.5988   $147.60   $147.60   $147.60  
  Purchase #6 $158.74   3.220%   $163.8514   $163.85   $163.85   $163.90  
  Purchase #7 $198.93   7.661%   $214.17   $214.17   $214.15   $214.20  
  7 purchase totals = $860.21       $926.0189   $926.02   $926.00   $926.10