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 $119.97   3.234%   $123.8498   $123.85   $123.85   $123.80  
  Purchase #2 $85.52   11.631%   $95.4668   $95.47   $95.45   $95.50  
  Purchase #3 $202.88   4.639%   $212.2916   $212.29   $212.30   $212.30  
  Purchase #4 $34.54   12.734%   $38.9383   $38.94   $38.95   $38.90  
  Purchase #5 $126.71   3.514%   $131.1626   $131.16   $131.15   $131.20  
  Purchase #6 $211.74   9.616%   $232.1009   $232.10   $232.10   $232.10  
  Purchase #7 $12.77   7.135%   $13.6811   $13.68   $13.70   $13.70  
  7 purchase totals = $794.13       $847.4911   $847.49   $847.50   $847.50