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 $154.28   5.663%   $163.0169   $163.02   $163.00   $163.00  
  Purchase #2 $102.80   9.623%   $112.6924   $112.69   $112.70   $112.70  
  Purchase #3 $162.61   8.822%   $176.9555   $176.96   $176.95   $177.00  
  Purchase #4 $123.41   8.649%   $134.0837   $134.08   $134.10   $134.10  
  Purchase #5 $190.35   5.749%   $201.2932   $201.29   $201.30   $201.30  
  Purchase #6 $68.31   10.831%   $75.7087   $75.71   $75.70   $75.70  
  Purchase #7 $202.30   13.173%   $228.949   $228.95   $228.95   $228.90  
  7 purchase totals = $1,004.06       $1,092.6994   $1,092.70   $1,092.70   $1,092.70