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 $65.25   7.570%   $70.1894   $70.19   $70.20   $70.20  
  Purchase #2 $150.41   7.315%   $161.4125   $161.41   $161.40   $161.40  
  Purchase #3 $181.35   6.628%   $193.3699   $193.37   $193.35   $193.40  
  Purchase #4 $114.95   11.598%   $128.2819   $128.28   $128.30   $128.30  
  Purchase #5 $10.44   8.728%   $11.3512   $11.35   $11.35   $11.40  
  Purchase #6 $237.37   10.482%   $262.2511   $262.25   $262.25   $262.30  
  Purchase #7 $216.46   3.409%   $223.8391   $223.84   $223.85   $223.80  
  7 purchase totals = $976.23       $1,050.6951   $1,050.69   $1,050.70   $1,050.80