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 $216.66   8.624%   $235.3448   $235.34   $235.35   $235.30  
  Purchase #2 $177.62   11.214%   $197.5383   $197.54   $197.55   $197.50  
  Purchase #3 $158.82   7.556%   $170.8204   $170.82   $170.80   $170.80  
  Purchase #4 $43.76   13.148%   $49.5136   $49.51   $49.50   $49.50  
  Purchase #5 $165.91   9.115%   $181.0327   $181.03   $181.05   $181.00  
  Purchase #6 $96.92   5.574%   $102.3223   $102.32   $102.30   $102.30  
  Purchase #7 $62.45   10.444%   $68.9723   $68.97   $68.95   $69.00  
  7 purchase totals = $922.14       $1,005.5444   $1,005.53   $1,005.50   $1,005.40