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 $60.43   6.782%   $64.5284   $64.53   $64.55   $64.50  
  Purchase #2 $153.58   12.204%   $172.3229   $172.32   $172.30   $172.30  
  Purchase #3 $113.72   5.302%   $119.7494   $119.75   $119.75   $119.70  
  Purchase #4 $26.28   9.702%   $28.8297   $28.83   $28.85   $28.80  
  Purchase #5 $189.51   7.545%   $203.8085   $203.81   $203.80   $203.80  
  Purchase #6 $29.54   13.751%   $33.602   $33.60   $33.60   $33.60  
  Purchase #7 $146.56   4.820%   $153.6242   $153.62   $153.60   $153.60  
  7 purchase totals = $719.62       $776.4651   $776.46   $776.45   $776.30