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 $243.49   10.795%   $269.7747   $269.77   $269.75   $269.80  
  Purchase #2 $136.31   13.195%   $154.2961   $154.30   $154.30   $154.30  
  Purchase #3 $199.42   10.144%   $219.6492   $219.65   $219.65   $219.60  
  Purchase #4 $37.60   9.195%   $41.0573   $41.06   $41.05   $41.10  
  Purchase #5 $162.83   6.326%   $173.1306   $173.13   $173.15   $173.10  
  Purchase #6 $218.33   6.308%   $232.1023   $232.10   $232.10   $232.10  
  Purchase #7 $21.76   13.471%   $24.6913   $24.69   $24.70   $24.70  
  7 purchase totals = $1,019.74       $1,114.7015   $1,114.70   $1,114.70   $1,114.70