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 $56.41   9.697%   $61.8801   $61.88   $61.90   $61.90  
  Purchase #2 $160.47   5.588%   $169.4371   $169.44   $169.45   $169.40  
  Purchase #3 $25.57   5.739%   $27.0375   $27.04   $27.05   $27.00  
  Purchase #4 $69.74   4.783%   $73.0757   $73.08   $73.10   $73.10  
  Purchase #5 $198.62   7.591%   $213.6972   $213.70   $213.70   $213.70  
  Purchase #6 $190.52   10.473%   $210.4732   $210.47   $210.45   $210.50  
  Purchase #7 $191.44   4.572%   $200.1926   $200.19   $200.20   $200.20  
  7 purchase totals = $892.77       $955.7934   $955.80   $955.85   $955.80