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 $130.51   5.820%   $138.1057   $138.11   $138.10   $138.10  
  Purchase #2 $156.76   9.825%   $172.1617   $172.16   $172.15   $172.20  
  Purchase #3 $105.56   12.329%   $118.5745   $118.57   $118.55   $118.60  
  Purchase #4 $68.33   5.640%   $72.1838   $72.18   $72.20   $72.20  
  Purchase #5 $95.37   13.563%   $108.305   $108.31   $108.30   $108.30  
  Purchase #6 $175.59   11.393%   $195.595   $195.60   $195.60   $195.60  
  Purchase #7 $226.74   9.301%   $247.8291   $247.83   $247.85   $247.80  
  7 purchase totals = $958.86       $1,052.7548   $1,052.76   $1,052.75   $1,052.80