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 $12.97   13.534%   $14.7254   $14.73   $14.75   $14.70  
  Purchase #2 $241.67   11.309%   $269.0005   $269.00   $269.00   $269.00  
  Purchase #3 $5.46   9.638%   $5.9862   $5.99   $6.00   $6.00  
  Purchase #4 $85.57   9.457%   $93.6624   $93.66   $93.65   $93.70  
  Purchase #5 $129.94   11.312%   $144.6388   $144.64   $144.65   $144.60  
  Purchase #6 $208.29   5.334%   $219.4002   $219.40   $219.40   $219.40  
  Purchase #7 $190.86   5.259%   $200.8973   $200.90   $200.90   $200.90  
  7 purchase totals = $874.76       $948.3108   $948.32   $948.35   $948.30