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 $29.27   10.839%   $32.4426   $32.44   $32.45   $32.40  
  Purchase #2 $239.96   13.603%   $272.6018   $272.60   $272.60   $272.60  
  Purchase #3 $154.76   11.462%   $172.4986   $172.50   $172.50   $172.50  
  Purchase #4 $169.27   10.657%   $187.3091   $187.31   $187.30   $187.30  
  Purchase #5 $196.94   10.295%   $217.215   $217.22   $217.20   $217.20  
  Purchase #6 $235.77   10.853%   $261.3581   $261.36   $261.35   $261.40  
  Purchase #7 $202.39   8.592%   $219.7793   $219.78   $219.80   $219.80  
  7 purchase totals = $1,228.36       $1,363.2045   $1,363.21   $1,363.20   $1,363.20