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 $74.39   8.787%   $80.9266   $80.93   $80.95   $80.90  
  Purchase #2 $31.80   6.247%   $33.7865   $33.79   $33.80   $33.80  
  Purchase #3 $199.54   6.532%   $212.574   $212.57   $212.55   $212.60  
  Purchase #4 $74.83   8.546%   $81.225   $81.23   $81.25   $81.20  
  Purchase #5 $108.36   7.600%   $116.5954   $116.60   $116.60   $116.60  
  Purchase #6 $145.86   3.491%   $150.952   $150.95   $150.95   $151.00  
  Purchase #7 $158.37   11.466%   $176.5287   $176.53   $176.55   $176.50  
  7 purchase totals = $793.15       $852.5882   $852.60   $852.65   $852.60