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 $229.75   12.764%   $259.0753   $259.08   $259.10   $259.10  
  Purchase #2 $233.88   12.732%   $263.6576   $263.66   $263.65   $263.70  
  Purchase #3 $34.76   13.183%   $39.3424   $39.34   $39.35   $39.30  
  Purchase #4 $215.61   7.828%   $232.488   $232.49   $232.50   $232.50  
  Purchase #5 $127.57   5.780%   $134.9435   $134.94   $134.95   $134.90  
  Purchase #6 $135.50   10.434%   $149.6381   $149.64   $149.65   $149.60  
  Purchase #7 $169.82   3.614%   $175.9573   $175.96   $175.95   $176.00  
  7 purchase totals = $1,146.89       $1,255.1022   $1,255.11   $1,255.15   $1,255.10