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 $61.58   4.685%   $64.465   $64.47   $64.45   $64.50  
  Purchase #2 $171.64   5.276%   $180.6957   $180.70   $180.70   $180.70  
  Purchase #3 $239.51   9.678%   $262.6898   $262.69   $262.70   $262.70  
  Purchase #4 $184.40   9.826%   $202.5191   $202.52   $202.50   $202.50  
  Purchase #5 $153.75   11.685%   $171.7157   $171.72   $171.70   $171.70  
  Purchase #6 $233.49   7.256%   $250.432   $250.43   $250.45   $250.40  
  Purchase #7 $165.29   11.377%   $184.095   $184.10   $184.10   $184.10  
  7 purchase totals = $1,209.66       $1,316.6123   $1,316.63   $1,316.60   $1,316.60