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 $188.88   6.836%   $201.7918   $201.79   $201.80   $201.80  
  Purchase #2 $179.73   9.449%   $196.7127   $196.71   $196.70   $196.70  
  Purchase #3 $52.53   11.532%   $58.5878   $58.59   $58.60   $58.60  
  Purchase #4 $126.82   6.614%   $135.2079   $135.21   $135.20   $135.20  
  Purchase #5 $242.45   8.665%   $263.4583   $263.46   $263.45   $263.50  
  Purchase #6 $169.74   6.799%   $181.2806   $181.28   $181.30   $181.30  
  Purchase #7 $166.41   5.849%   $176.1433   $176.14   $176.15   $176.10  
  7 purchase totals = $1,126.56       $1,213.1824   $1,213.18   $1,213.20   $1,213.20