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 $181.44   11.705%   $202.6776   $202.68   $202.70   $202.70  
  Purchase #2 $231.94   11.738%   $259.1651   $259.17   $259.15   $259.20  
  Purchase #3 $165.66   4.172%   $172.5713   $172.57   $172.55   $172.60  
  Purchase #4 $126.44   7.701%   $136.1771   $136.18   $136.20   $136.20  
  Purchase #5 $193.45   8.497%   $209.8874   $209.89   $209.90   $209.90  
  Purchase #6 $24.70   11.405%   $27.517   $27.52   $27.50   $27.50  
  Purchase #7 $44.50   13.605%   $50.5542   $50.55   $50.55   $50.60  
  7 purchase totals = $968.13       $1,058.5497   $1,058.56   $1,058.55   $1,058.70