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 $205.86   13.506%   $233.6635   $233.66   $233.65   $233.70  
  Purchase #2 $27.67   3.189%   $28.5524   $28.55   $28.55   $28.60  
  Purchase #3 $167.90   9.764%   $184.2938   $184.29   $184.30   $184.30  
  Purchase #4 $130.41   10.325%   $143.8748   $143.87   $143.85   $143.90  
  Purchase #5 $96.31   6.822%   $102.8803   $102.88   $102.90   $102.90  
  Purchase #6 $41.64   5.608%   $43.9752   $43.98   $44.00   $44.00  
  Purchase #7 $206.37   11.608%   $230.3254   $230.33   $230.35   $230.30  
  7 purchase totals = $876.16       $967.5654   $967.56   $967.60   $967.70