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 $88.35   4.167%   $92.0315   $92.03   $92.05   $92.00  
  Purchase #2 $65.39   9.494%   $71.5981   $71.60   $71.60   $71.60  
  Purchase #3 $16.62   4.258%   $17.3277   $17.33   $17.35   $17.30  
  Purchase #4 $246.72   10.571%   $272.8008   $272.80   $272.80   $272.80  
  Purchase #5 $131.85   11.612%   $147.1604   $147.16   $147.15   $147.20  
  Purchase #6 $20.28   13.167%   $22.9503   $22.95   $22.95   $23.00  
  Purchase #7 $98.56   4.724%   $103.216   $103.22   $103.20   $103.20  
  7 purchase totals = $667.77       $727.0848   $727.09   $727.10   $727.10