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 $193.69   5.304%   $203.9633   $203.96   $203.95   $204.00  
  Purchase #2 $48.72   6.671%   $51.9701   $51.97   $51.95   $52.00  
  Purchase #3 $130.25   10.703%   $144.1907   $144.19   $144.20   $144.20  
  Purchase #4 $127.93   7.139%   $137.0629   $137.06   $137.05   $137.10  
  Purchase #5 $215.83   6.569%   $230.0079   $230.01   $230.00   $230.00  
  Purchase #6 $81.42   5.452%   $85.859   $85.86   $85.85   $85.90  
  Purchase #7 $161.79   12.162%   $181.4669   $181.47   $181.45   $181.50  
  7 purchase totals = $959.63       $1,034.5208   $1,034.52   $1,034.45   $1,034.70