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 $224.68   10.133%   $247.4468   $247.45   $247.45   $247.40  
  Purchase #2 $135.96   4.686%   $142.3311   $142.33   $142.35   $142.30  
  Purchase #3 $76.73   4.720%   $80.3517   $80.35   $80.35   $80.40  
  Purchase #4 $245.64   13.683%   $279.2509   $279.25   $279.25   $279.30  
  Purchase #5 $77.41   10.431%   $85.4846   $85.48   $85.50   $85.50  
  Purchase #6 $58.52   3.153%   $60.3651   $60.37   $60.35   $60.40  
  Purchase #7 $146.70   12.762%   $165.4219   $165.42   $165.40   $165.40  
  7 purchase totals = $965.64       $1,060.6521   $1,060.65   $1,060.65   $1,060.70