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 $218.36   10.482%   $241.2485   $241.25   $241.25   $241.20  
  Purchase #2 $164.72   7.699%   $177.4018   $177.40   $177.40   $177.40  
  Purchase #3 $32.48   3.406%   $33.5863   $33.59   $33.60   $33.60  
  Purchase #4 $133.88   9.813%   $147.0176   $147.02   $147.00   $147.00  
  Purchase #5 $209.47   7.814%   $225.838   $225.84   $225.85   $225.80  
  Purchase #6 $154.40   7.686%   $166.2672   $166.27   $166.25   $166.30  
  Purchase #7 $230.52   4.478%   $240.8427   $240.84   $240.85   $240.80  
  7 purchase totals = $1,143.83       $1,232.2021   $1,232.21   $1,232.20   $1,232.10