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 $167.54   9.246%   $183.0307   $183.03   $183.05   $183.00  
  Purchase #2 $232.98   13.554%   $264.5581   $264.56   $264.55   $264.60  
  Purchase #3 $56.75   7.596%   $61.0607   $61.06   $61.05   $61.10  
  Purchase #4 $163.48   10.304%   $180.325   $180.33   $180.35   $180.30  
  Purchase #5 $244.84   9.778%   $268.7805   $268.78   $268.80   $268.80  
  Purchase #6 $27.48   6.311%   $29.2143   $29.21   $29.20   $29.20  
  Purchase #7 $39.99   8.209%   $43.2728   $43.27   $43.25   $43.30  
  7 purchase totals = $933.06       $1,030.2421   $1,030.24   $1,030.25   $1,030.30