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 $120.97   4.651%   $126.5963   $126.60   $126.60   $126.60  
  Purchase #2 $158.65   6.720%   $169.3113   $169.31   $169.30   $169.30  
  Purchase #3 $149.46   8.397%   $162.0102   $162.01   $162.00   $162.00  
  Purchase #4 $70.31   4.821%   $73.6996   $73.70   $73.70   $73.70  
  Purchase #5 $158.94   4.116%   $165.482   $165.48   $165.50   $165.50  
  Purchase #6 $70.90   6.291%   $75.3603   $75.36   $75.35   $75.40  
  Purchase #7 $225.59   4.535%   $235.8205   $235.82   $235.80   $235.80  
  7 purchase totals = $954.82       $1,008.2802   $1,008.28   $1,008.25   $1,008.30