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 $68.65   7.275%   $73.6443   $73.64   $73.65   $73.60  
  Purchase #2 $147.42   7.401%   $158.3306   $158.33   $158.35   $158.30  
  Purchase #3 $203.46   10.529%   $224.8823   $224.88   $224.90   $224.90  
  Purchase #4 $64.69   6.129%   $68.6549   $68.65   $68.65   $68.70  
  Purchase #5 $203.27   11.631%   $226.9123   $226.91   $226.90   $226.90  
  Purchase #6 $134.90   13.831%   $153.558   $153.56   $153.55   $153.60  
  Purchase #7 $140.82   6.680%   $150.2268   $150.23   $150.25   $150.20  
  7 purchase totals = $963.21       $1,056.2092   $1,056.20   $1,056.25   $1,056.20