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 $55.49   7.691%   $59.7577   $59.76   $59.75   $59.80  
  Purchase #2 $245.83   12.220%   $275.8704   $275.87   $275.85   $275.90  
  Purchase #3 $54.42   6.190%   $57.7886   $57.79   $57.80   $57.80  
  Purchase #4 $189.35   10.435%   $209.1087   $209.11   $209.10   $209.10  
  Purchase #5 $218.81   9.276%   $239.1068   $239.11   $239.10   $239.10  
  Purchase #6 $221.88   8.856%   $241.5297   $241.53   $241.55   $241.50  
  Purchase #7 $169.72   4.651%   $177.6137   $177.61   $177.60   $177.60  
  7 purchase totals = $1,155.50       $1,260.7756   $1,260.78   $1,260.75   $1,260.80