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 $206.61   13.183%   $233.8474   $233.85   $233.85   $233.80  
  Purchase #2 $135.56   8.703%   $147.3578   $147.36   $147.35   $147.40  
  Purchase #3 $44.65   5.154%   $46.9513   $46.95   $46.95   $47.00  
  Purchase #4 $165.87   7.150%   $177.7297   $177.73   $177.75   $177.70  
  Purchase #5 $119.61   5.783%   $126.527   $126.53   $126.55   $126.50  
  Purchase #6 $90.74   12.736%   $102.2966   $102.30   $102.30   $102.30  
  Purchase #7 $84.83   7.713%   $91.3729   $91.37   $91.35   $91.40  
  7 purchase totals = $847.87       $926.0827   $926.09   $926.10   $926.10