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 $153.34   13.589%   $174.1774   $174.18   $174.20   $174.20  
  Purchase #2 $241.70   11.834%   $270.3028   $270.30   $270.30   $270.30  
  Purchase #3 $97.83   6.619%   $104.3054   $104.31   $104.30   $104.30  
  Purchase #4 $163.94   6.409%   $174.4469   $174.45   $174.45   $174.40  
  Purchase #5 $83.56   9.548%   $91.5383   $91.54   $91.55   $91.50  
  Purchase #6 $163.81   7.705%   $176.4316   $176.43   $176.45   $176.40  
  Purchase #7 $60.70   13.210%   $68.7185   $68.72   $68.70   $68.70  
  7 purchase totals = $964.88       $1,059.9209   $1,059.93   $1,059.95   $1,059.80