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 $69.41   9.301%   $75.8658   $75.87   $75.85   $75.90  
  Purchase #2 $35.55   10.702%   $39.3546   $39.35   $39.35   $39.40  
  Purchase #3 $217.49   13.331%   $246.4836   $246.48   $246.50   $246.50  
  Purchase #4 $205.44   9.222%   $224.3857   $224.39   $224.40   $224.40  
  Purchase #5 $103.72   10.411%   $114.5183   $114.52   $114.50   $114.50  
  Purchase #6 $122.87   10.174%   $135.3708   $135.37   $135.35   $135.40  
  Purchase #7 $210.32   6.490%   $223.9698   $223.97   $223.95   $224.00  
  7 purchase totals = $964.80       $1,059.9486   $1,059.95   $1,059.90   $1,060.10