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 $88.84   6.170%   $94.3214   $94.32   $94.30   $94.30  
  Purchase #2 $121.42   4.488%   $126.8693   $126.87   $126.85   $126.90  
  Purchase #3 $162.84   7.294%   $174.7175   $174.72   $174.70   $174.70  
  Purchase #4 $92.76   3.212%   $95.7395   $95.74   $95.75   $95.70  
  Purchase #5 $56.74   6.756%   $60.5734   $60.57   $60.55   $60.60  
  Purchase #6 $234.48   7.873%   $252.9406   $252.94   $252.95   $252.90  
  Purchase #7 $77.53   3.793%   $80.4707   $80.47   $80.45   $80.50  
  7 purchase totals = $834.61       $885.6324   $885.63   $885.55   $885.60