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 $83.39   13.653%   $94.7752   $94.78   $94.80   $94.80  
  Purchase #2 $115.32   9.609%   $126.4011   $126.40   $126.40   $126.40  
  Purchase #3 $201.44   10.685%   $222.9639   $222.96   $222.95   $223.00  
  Purchase #4 $138.48   4.350%   $144.5039   $144.50   $144.50   $144.50  
  Purchase #5 $173.89   6.518%   $185.2242   $185.22   $185.20   $185.20  
  Purchase #6 $188.81   9.763%   $207.2435   $207.24   $207.25   $207.20  
  Purchase #7 $58.57   13.599%   $66.5349   $66.53   $66.55   $66.50  
  7 purchase totals = $959.90       $1,047.6467   $1,047.63   $1,047.65   $1,047.60