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 $205.94   9.269%   $225.0286   $225.03   $225.05   $225.00  
  Purchase #2 $61.34   9.616%   $67.2385   $67.24   $67.25   $67.20  
  Purchase #3 $191.65   8.527%   $207.992   $207.99   $208.00   $208.00  
  Purchase #4 $45.82   8.155%   $49.5566   $49.56   $49.55   $49.60  
  Purchase #5 $223.35   12.466%   $251.1928   $251.19   $251.20   $251.20  
  Purchase #6 $108.95   10.469%   $120.356   $120.36   $120.35   $120.40  
  Purchase #7 $121.45   13.281%   $137.5798   $137.58   $137.60   $137.60  
  7 purchase totals = $958.50       $1,058.9443   $1,058.95   $1,059.00   $1,059.00