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 $250.39   13.308%   $283.7119   $283.71   $283.70   $283.70  
  Purchase #2 $41.45   4.364%   $43.2589   $43.26   $43.25   $43.30  
  Purchase #3 $41.39   8.358%   $44.8494   $44.85   $44.85   $44.80  
  Purchase #4 $239.74   7.352%   $257.3657   $257.37   $257.35   $257.40  
  Purchase #5 $120.92   8.638%   $131.3651   $131.37   $131.35   $131.40  
  Purchase #6 $204.74   11.222%   $227.7159   $227.72   $227.70   $227.70  
  Purchase #7 $20.72   12.370%   $23.2831   $23.28   $23.30   $23.30  
  7 purchase totals = $919.35       $1,011.5500   $1,011.56   $1,011.50   $1,011.60