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 $246.73   9.297%   $269.6685   $269.67   $269.65   $269.70  
  Purchase #2 $124.61   9.418%   $136.3458   $136.35   $136.35   $136.30  
  Purchase #3 $210.40   6.610%   $224.3074   $224.31   $224.30   $224.30  
  Purchase #4 $234.83   13.388%   $266.269   $266.27   $266.25   $266.30  
  Purchase #5 $43.30   7.183%   $46.4102   $46.41   $46.40   $46.40  
  Purchase #6 $250.52   7.138%   $268.4021   $268.40   $268.40   $268.40  
  Purchase #7 $230.72   9.413%   $252.4377   $252.44   $252.45   $252.40  
  7 purchase totals = $1,341.11       $1,463.8407   $1,463.85   $1,463.80   $1,463.80