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 $243.41   11.317%   $270.9567   $270.96   $270.95   $271.00  
  Purchase #2 $90.51   4.481%   $94.5658   $94.57   $94.55   $94.60  
  Purchase #3 $138.96   8.657%   $150.9898   $150.99   $151.00   $151.00  
  Purchase #4 $207.85   11.323%   $231.3849   $231.38   $231.40   $231.40  
  Purchase #5 $167.53   8.848%   $182.3531   $182.35   $182.35   $182.40  
  Purchase #6 $231.34   12.844%   $261.0533   $261.05   $261.05   $261.10  
  Purchase #7 $162.67   5.203%   $171.1337   $171.13   $171.15   $171.10  
  7 purchase totals = $1,242.27       $1,362.4373   $1,362.43   $1,362.45   $1,362.60