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 $217.77   4.705%   $228.0161   $228.02   $228.00   $228.00  
  Purchase #2 $103.41   9.613%   $113.3508   $113.35   $113.35   $113.40  
  Purchase #3 $241.43   6.640%   $257.461   $257.46   $257.45   $257.50  
  Purchase #4 $204.83   13.579%   $232.6439   $232.64   $232.65   $232.60  
  Purchase #5 $107.31   13.629%   $121.9353   $121.94   $121.95   $121.90  
  Purchase #6 $168.81   8.656%   $183.4222   $183.42   $183.40   $183.40  
  Purchase #7 $76.71   5.421%   $80.8684   $80.87   $80.85   $80.90  
  7 purchase totals = $1,120.27       $1,217.6977   $1,217.70   $1,217.65   $1,217.70