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 $53.33   6.289%   $56.6839   $56.68   $56.70   $56.70  
  Purchase #2 $120.38   3.319%   $124.3754   $124.38   $124.40   $124.40  
  Purchase #3 $136.78   10.452%   $151.0762   $151.08   $151.10   $151.10  
  Purchase #4 $119.72   12.592%   $134.7951   $134.80   $134.80   $134.80  
  Purchase #5 $22.56   3.219%   $23.2862   $23.29   $23.30   $23.30  
  Purchase #6 $203.89   6.814%   $217.7831   $217.78   $217.80   $217.80  
  Purchase #7 $128.44   10.226%   $141.5743   $141.57   $141.55   $141.60  
  7 purchase totals = $785.10       $849.5742   $849.58   $849.65   $849.70