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 $32.57   4.276%   $33.9627   $33.96   $33.95   $34.00  
  Purchase #2 $149.93   6.299%   $159.3741   $159.37   $159.35   $159.40  
  Purchase #3 $138.90   12.479%   $156.2333   $156.23   $156.25   $156.20  
  Purchase #4 $211.32   9.340%   $231.0573   $231.06   $231.05   $231.10  
  Purchase #5 $54.58   7.153%   $58.4841   $58.48   $58.50   $58.50  
  Purchase #6 $181.26   7.341%   $194.5663   $194.57   $194.55   $194.60  
  Purchase #7 $164.73   4.798%   $172.6337   $172.63   $172.65   $172.60  
  7 purchase totals = $933.29       $1,006.3115   $1,006.30   $1,006.30   $1,006.40