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 $124.27   13.524%   $141.0763   $141.08   $141.10   $141.10  
  Purchase #2 $214.33   8.212%   $231.9308   $231.93   $231.95   $231.90  
  Purchase #3 $158.49   4.579%   $165.7473   $165.75   $165.75   $165.70  
  Purchase #4 $59.30   13.731%   $67.4425   $67.44   $67.45   $67.40  
  Purchase #5 $203.40   8.646%   $220.986   $220.99   $221.00   $221.00  
  Purchase #6 $229.61   12.241%   $257.7166   $257.72   $257.70   $257.70  
  Purchase #7 $236.70   12.303%   $265.8212   $265.82   $265.80   $265.80  
  7 purchase totals = $1,226.10       $1,350.7207   $1,350.73   $1,350.75   $1,350.60