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 $62.95   3.392%   $65.0853   $65.09   $65.10   $65.10  
  Purchase #2 $45.76   10.488%   $50.5593   $50.56   $50.55   $50.60  
  Purchase #3 $109.36   12.194%   $122.6954   $122.70   $122.70   $122.70  
  Purchase #4 $209.56   4.656%   $219.3171   $219.32   $219.30   $219.30  
  Purchase #5 $147.37   4.278%   $153.6745   $153.67   $153.65   $153.70  
  Purchase #6 $192.39   5.161%   $202.3192   $202.32   $202.30   $202.30  
  Purchase #7 $207.69   9.131%   $226.6542   $226.65   $226.65   $226.70  
  7 purchase totals = $975.08       $1,040.3050   $1,040.31   $1,040.25   $1,040.40