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 $77.87   3.143%   $80.3175   $80.32   $80.30   $80.30  
  Purchase #2 $194.64   3.474%   $201.4018   $201.40   $201.40   $201.40  
  Purchase #3 $123.70   8.702%   $134.4644   $134.46   $134.45   $134.50  
  Purchase #4 $232.29   11.470%   $258.9337   $258.93   $258.95   $258.90  
  Purchase #5 $149.61   5.544%   $157.9044   $157.90   $157.90   $157.90  
  Purchase #6 $98.39   11.800%   $110   $110.00   $110.00   $110.00  
  Purchase #7 $82.45   10.673%   $91.2499   $91.25   $91.25   $91.20  
  7 purchase totals = $958.95       $1,034.2717   $1,034.26   $1,034.25   $1,034.20