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 $187.91   10.121%   $206.9284   $206.93   $206.95   $206.90  
  Purchase #2 $202.87   9.113%   $221.3575   $221.36   $221.35   $221.40  
  Purchase #3 $225.52   7.418%   $242.2491   $242.25   $242.25   $242.20  
  Purchase #4 $62.92   5.165%   $66.1698   $66.17   $66.15   $66.20  
  Purchase #5 $226.36   9.373%   $247.5767   $247.58   $247.60   $247.60  
  Purchase #6 $11.46   9.673%   $12.5685   $12.57   $12.55   $12.60  
  Purchase #7 $190.31   6.742%   $203.1407   $203.14   $203.15   $203.10  
  7 purchase totals = $1,107.35       $1,199.9907   $1,200.00   $1,200.00   $1,200.00