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 $22.66   11.436%   $25.2514   $25.25   $25.25   $25.30  
  Purchase #2 $246.87   11.793%   $275.9834   $275.98   $276.00   $276.00  
  Purchase #3 $45.46   9.211%   $49.6473   $49.65   $49.65   $49.60  
  Purchase #4 $214.84   3.861%   $223.135   $223.14   $223.15   $223.10  
  Purchase #5 $152.66   7.714%   $164.4362   $164.44   $164.45   $164.40  
  Purchase #6 $202.79   8.524%   $220.0758   $220.08   $220.10   $220.10  
  Purchase #7 $72.28   3.661%   $74.9262   $74.93   $74.95   $74.90  
  7 purchase totals = $957.56       $1,033.4553   $1,033.47   $1,033.55   $1,033.40