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 $63.98   8.840%   $69.6358   $69.64   $69.65   $69.60  
  Purchase #2 $206.32   12.137%   $231.3611   $231.36   $231.35   $231.40  
  Purchase #3 $241.37   4.705%   $252.7265   $252.73   $252.75   $252.70  
  Purchase #4 $10.36   11.640%   $11.5659   $11.57   $11.55   $11.60  
  Purchase #5 $48.99   3.717%   $50.811   $50.81   $50.80   $50.80  
  Purchase #6 $155.45   3.550%   $160.9685   $160.97   $160.95   $161.00  
  Purchase #7 $243.46   13.216%   $275.6357   $275.64   $275.65   $275.60  
  7 purchase totals = $969.93       $1,052.7045   $1,052.72   $1,052.70   $1,052.70