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 $243.32   6.518%   $259.1796   $259.18   $259.20   $259.20  
  Purchase #2 $175.41   6.561%   $186.9187   $186.92   $186.90   $186.90  
  Purchase #3 $56.70   11.688%   $63.3271   $63.33   $63.35   $63.30  
  Purchase #4 $92.71   8.571%   $100.6562   $100.66   $100.65   $100.70  
  Purchase #5 $203.97   5.826%   $215.8533   $215.85   $215.85   $215.90  
  Purchase #6 $97.62   6.353%   $103.8218   $103.82   $103.80   $103.80  
  Purchase #7 $127.55   12.261%   $143.1889   $143.19   $143.20   $143.20  
  7 purchase totals = $997.28       $1,072.9456   $1,072.95   $1,072.95   $1,073.00