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 $59.67   4.676%   $62.4602   $62.46   $62.45   $62.50  
  Purchase #2 $94.38   8.102%   $102.0267   $102.03   $102.05   $102.00  
  Purchase #3 $52.70   5.798%   $55.7555   $55.76   $55.75   $55.80  
  Purchase #4 $175.80   8.421%   $190.6041   $190.60   $190.60   $190.60  
  Purchase #5 $186.52   8.747%   $202.8349   $202.83   $202.85   $202.80  
  Purchase #6 $157.32   5.365%   $165.7602   $165.76   $165.75   $165.80  
  Purchase #7 $184.33   11.514%   $205.5538   $205.55   $205.55   $205.60  
  7 purchase totals = $910.72       $984.9954   $984.99   $985.00   $985.10