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 $180.58   13.524%   $205.0016   $205.00   $205.00   $205.00  
  Purchase #2 $221.90   3.237%   $229.0829   $229.08   $229.10   $229.10  
  Purchase #3 $160.92   11.479%   $179.392   $179.39   $179.40   $179.40  
  Purchase #4 $86.71   12.371%   $97.4369   $97.44   $97.45   $97.40  
  Purchase #5 $157.73   8.779%   $171.5771   $171.58   $171.60   $171.60  
  Purchase #6 $165.55   9.639%   $181.5074   $181.51   $181.50   $181.50  
  Purchase #7 $218.90   8.653%   $237.8414   $237.84   $237.85   $237.80  
  7 purchase totals = $1,192.29       $1,301.8393   $1,301.84   $1,301.90   $1,301.80