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 $33.66   6.208%   $35.7496   $35.75   $35.75   $35.70  
  Purchase #2 $243.66   13.175%   $275.7622   $275.76   $275.75   $275.80  
  Purchase #3 $49.62   5.204%   $52.2022   $52.20   $52.20   $52.20  
  Purchase #4 $153.59   12.391%   $172.6213   $172.62   $172.60   $172.60  
  Purchase #5 $219.86   5.681%   $232.3502   $232.35   $232.35   $232.40  
  Purchase #6 $178.35   5.250%   $187.7134   $187.71   $187.70   $187.70  
  Purchase #7 $187.96   13.832%   $213.9586   $213.96   $213.95   $214.00  
  7 purchase totals = $1,066.70       $1,170.3575   $1,170.35   $1,170.30   $1,170.40