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 $85.60   12.662%   $96.4387   $96.44   $96.45   $96.40  
  Purchase #2 $214.62   4.834%   $224.9947   $224.99   $225.00   $225.00  
  Purchase #3 $134.91   10.592%   $149.1997   $149.20   $149.20   $149.20  
  Purchase #4 $138.84   8.653%   $150.8538   $150.85   $150.85   $150.90  
  Purchase #5 $67.97   9.442%   $74.3877   $74.39   $74.40   $74.40  
  Purchase #6 $78.45   13.820%   $89.2918   $89.29   $89.30   $89.30  
  Purchase #7 $105.61   10.344%   $116.5343   $116.53   $116.55   $116.50  
  7 purchase totals = $826.00       $901.7007   $901.69   $901.75   $901.70