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 $123.89   9.740%   $135.9569   $135.96   $135.95   $136.00  
  Purchase #2 $136.42   9.712%   $149.6691   $149.67   $149.65   $149.70  
  Purchase #3 $192.87   7.644%   $207.613   $207.61   $207.60   $207.60  
  Purchase #4 $163.34   8.206%   $176.7437   $176.74   $176.75   $176.70  
  Purchase #5 $184.29   6.561%   $196.3813   $196.38   $196.40   $196.40  
  Purchase #6 $221.37   6.393%   $235.5222   $235.52   $235.50   $235.50  
  Purchase #7 $12.49   7.369%   $13.4104   $13.41   $13.40   $13.40  
  7 purchase totals = $1,034.67       $1,115.2966   $1,115.29   $1,115.25   $1,115.30