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 $246.32   3.731%   $255.5102   $255.51   $255.50   $255.50  
  Purchase #2 $192.94   6.539%   $205.5563   $205.56   $205.55   $205.60  
  Purchase #3 $99.95   13.170%   $113.1134   $113.11   $113.10   $113.10  
  Purchase #4 $178.55   5.672%   $188.6774   $188.68   $188.70   $188.70  
  Purchase #5 $173.30   6.536%   $184.6269   $184.63   $184.65   $184.60  
  Purchase #6 $59.47   12.692%   $67.0179   $67.02   $67.00   $67.00  
  Purchase #7 $218.79   5.850%   $231.5892   $231.59   $231.60   $231.60  
  7 purchase totals = $1,169.32       $1,246.0913   $1,246.10   $1,246.10   $1,246.10