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 $54.81   10.719%   $60.6851   $60.69   $60.70   $60.70  
  Purchase #2 $142.29   5.681%   $150.3735   $150.37   $150.35   $150.40  
  Purchase #3 $28.90   6.536%   $30.7889   $30.79   $30.80   $30.80  
  Purchase #4 $78.63   11.310%   $87.5231   $87.52   $87.50   $87.50  
  Purchase #5 $10.99   6.274%   $11.6795   $11.68   $11.70   $11.70  
  Purchase #6 $163.27   12.308%   $183.3653   $183.37   $183.35   $183.40  
  Purchase #7 $227.56   4.685%   $238.2212   $238.22   $238.20   $238.20  
  7 purchase totals = $706.45       $762.6366   $762.64   $762.60   $762.70