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 $65.35   3.659%   $67.7412   $67.74   $67.75   $67.70  
  Purchase #2 $189.25   10.258%   $208.6633   $208.66   $208.65   $208.70  
  Purchase #3 $220.90   7.658%   $237.8165   $237.82   $237.80   $237.80  
  Purchase #4 $71.35   4.785%   $74.7641   $74.76   $74.75   $74.80  
  Purchase #5 $53.74   9.415%   $58.7996   $58.80   $58.80   $58.80  
  Purchase #6 $163.43   11.118%   $181.6001   $181.60   $181.60   $181.60  
  Purchase #7 $22.92   5.696%   $24.2255   $24.23   $24.25   $24.20  
  7 purchase totals = $786.94       $853.6103   $853.61   $853.60   $853.60