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 $54.98   8.419%   $59.6088   $59.61   $59.60   $59.60  
  Purchase #2 $172.62   6.448%   $183.7505   $183.75   $183.75   $183.80  
  Purchase #3 $27.39   9.233%   $29.9189   $29.92   $29.90   $29.90  
  Purchase #4 $160.45   12.829%   $181.0341   $181.03   $181.05   $181.00  
  Purchase #5 $149.91   6.617%   $159.8295   $159.83   $159.85   $159.80  
  Purchase #6 $239.35   11.805%   $267.6053   $267.61   $267.60   $267.60  
  Purchase #7 $116.41   13.388%   $131.995   $132.00   $132.00   $132.00  
  7 purchase totals = $921.11       $1,013.7421   $1,013.75   $1,013.75   $1,013.70