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 $197.55   8.305%   $213.9565   $213.96   $213.95   $214.00  
  Purchase #2 $120.77   12.727%   $136.1404   $136.14   $136.15   $136.10  
  Purchase #3 $32.81   3.578%   $33.9839   $33.98   $34.00   $34.00  
  Purchase #4 $175.74   4.162%   $183.0543   $183.05   $183.05   $183.10  
  Purchase #5 $201.52   4.444%   $210.4755   $210.48   $210.50   $210.50  
  Purchase #6 $102.40   5.522%   $108.0545   $108.05   $108.05   $108.10  
  Purchase #7 $167.64   6.531%   $178.5886   $178.59   $178.60   $178.60  
  7 purchase totals = $998.43       $1,064.2537   $1,064.25   $1,064.30   $1,064.40