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 $228.67   7.845%   $246.6092   $246.61   $246.60   $246.60  
  Purchase #2 $79.77   7.300%   $85.5932   $85.59   $85.60   $85.60  
  Purchase #3 $171.70   9.583%   $188.154   $188.15   $188.15   $188.20  
  Purchase #4 $84.68   13.146%   $95.812   $95.81   $95.80   $95.80  
  Purchase #5 $156.43   11.501%   $174.421   $174.42   $174.40   $174.40  
  Purchase #6 $131.52   6.604%   $140.2056   $140.21   $140.20   $140.20  
  Purchase #7 $50.96   9.671%   $55.8883   $55.89   $55.90   $55.90  
  7 purchase totals = $903.73       $986.6833   $986.68   $986.65   $986.70