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 $175.37   5.267%   $184.6067   $184.61   $184.60   $184.60  
  Purchase #2 $30.61   9.102%   $33.3961   $33.40   $33.40   $33.40  
  Purchase #3 $155.58   9.185%   $169.87   $169.87   $169.85   $169.90  
  Purchase #4 $15.32   8.233%   $16.5813   $16.58   $16.60   $16.60  
  Purchase #5 $85.27   10.251%   $94.011   $94.01   $94.00   $94.00  
  Purchase #6 $248.65   9.280%   $271.7247   $271.72   $271.70   $271.70  
  Purchase #7 $228.68   12.125%   $256.4075   $256.41   $256.40   $256.40  
  7 purchase totals = $939.48       $1,026.5973   $1,026.60   $1,026.55   $1,026.60