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 $113.30   11.741%   $126.6026   $126.60   $126.60   $126.60  
  Purchase #2 $155.79   13.589%   $176.9603   $176.96   $176.95   $177.00  
  Purchase #3 $43.84   11.754%   $48.993   $48.99   $49.00   $49.00  
  Purchase #4 $233.94   3.258%   $241.5618   $241.56   $241.55   $241.60  
  Purchase #5 $222.95   9.379%   $243.8605   $243.86   $243.85   $243.90  
  Purchase #6 $22.67   8.504%   $24.5979   $24.60   $24.60   $24.60  
  Purchase #7 $188.73   3.517%   $195.3676   $195.37   $195.35   $195.40  
  7 purchase totals = $981.22       $1,057.9437   $1,057.94   $1,057.90   $1,058.10