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 $60.92   9.836%   $66.9121   $66.91   $66.90   $66.90  
  Purchase #2 $155.94   12.329%   $175.1658   $175.17   $175.15   $175.20  
  Purchase #3 $77.66   3.276%   $80.2041   $80.20   $80.20   $80.20  
  Purchase #4 $149.82   7.760%   $161.446   $161.45   $161.45   $161.40  
  Purchase #5 $204.55   3.173%   $211.0404   $211.04   $211.05   $211.00  
  Purchase #6 $99.49   6.414%   $105.8713   $105.87   $105.85   $105.90  
  Purchase #7 $76.26   8.719%   $82.9091   $82.91   $82.90   $82.90  
  7 purchase totals = $824.64       $883.5488   $883.55   $883.50   $883.50