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 $64.94   7.167%   $69.5942   $69.59   $69.60   $69.60  
  Purchase #2 $9.94   9.108%   $10.8453   $10.85   $10.85   $10.80  
  Purchase #3 $245.81   7.499%   $264.2433   $264.24   $264.25   $264.20  
  Purchase #4 $127.46   4.605%   $133.3295   $133.33   $133.35   $133.30  
  Purchase #5 $197.91   4.819%   $207.4473   $207.45   $207.45   $207.40  
  Purchase #6 $200.49   11.505%   $223.5564   $223.56   $223.55   $223.60  
  Purchase #7 $29.26   8.246%   $31.6728   $31.67   $31.65   $31.70  
  7 purchase totals = $875.81       $940.6888   $940.69   $940.70   $940.60