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 $128.83   13.124%   $145.7376   $145.74   $145.75   $145.70  
  Purchase #2 $168.29   8.747%   $183.0103   $183.01   $183.00   $183.00  
  Purchase #3 $235.29   3.571%   $243.6922   $243.69   $243.70   $243.70  
  Purchase #4 $144.83   7.861%   $156.2151   $156.22   $156.20   $156.20  
  Purchase #5 $44.99   10.224%   $49.5898   $49.59   $49.60   $49.60  
  Purchase #6 $212.55   10.365%   $234.5808   $234.58   $234.60   $234.60  
  Purchase #7 $216.49   11.168%   $240.6676   $240.67   $240.65   $240.70  
  7 purchase totals = $1,151.27       $1,253.4934   $1,253.50   $1,253.50   $1,253.50