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 $30.31   12.326%   $34.046   $34.05   $34.05   $34.00  
  Purchase #2 $59.65   13.320%   $67.5954   $67.60   $67.60   $67.60  
  Purchase #3 $112.31   6.604%   $119.727   $119.73   $119.75   $119.70  
  Purchase #4 $172.80   11.387%   $192.4767   $192.48   $192.50   $192.50  
  Purchase #5 $118.73   7.591%   $127.7428   $127.74   $127.75   $127.70  
  Purchase #6 $244.43   3.169%   $252.176   $252.18   $252.20   $252.20  
  Purchase #7 $29.37   12.430%   $33.0207   $33.02   $33.00   $33.00  
  7 purchase totals = $767.60       $826.7846   $826.80   $826.85   $826.70