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 $99.26   3.550%   $102.7837   $102.78   $102.80   $102.80  
  Purchase #2 $167.59   9.287%   $183.1541   $183.15   $183.15   $183.20  
  Purchase #3 $172.88   6.181%   $183.5657   $183.57   $183.55   $183.60  
  Purchase #4 $181.71   7.759%   $195.8089   $195.81   $195.80   $195.80  
  Purchase #5 $92.47   3.309%   $95.5298   $95.53   $95.55   $95.50  
  Purchase #6 $220.91   6.637%   $235.5718   $235.57   $235.55   $235.60  
  Purchase #7 $92.29   11.167%   $102.596   $102.60   $102.60   $102.60  
  7 purchase totals = $1,027.11       $1,099.0100   $1,099.01   $1,099.00   $1,099.10