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 $129.30   7.319%   $138.7635   $138.76   $138.75   $138.80  
  Purchase #2 $81.60   9.368%   $89.2443   $89.24   $89.25   $89.20  
  Purchase #3 $95.65   10.364%   $105.5632   $105.56   $105.55   $105.60  
  Purchase #4 $77.57   8.816%   $84.4086   $84.41   $84.40   $84.40  
  Purchase #5 $49.67   6.585%   $52.9408   $52.94   $52.95   $52.90  
  Purchase #6 $243.96   7.208%   $261.5446   $261.54   $261.55   $261.50  
  Purchase #7 $221.60   8.478%   $240.3872   $240.39   $240.40   $240.40  
  7 purchase totals = $899.35       $972.8522   $972.84   $972.85   $972.80