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 $147.27   8.663%   $160.028   $160.03   $160.05   $160.00  
  Purchase #2 $213.35   4.225%   $222.364   $222.36   $222.35   $222.40  
  Purchase #3 $153.50   13.560%   $174.3146   $174.31   $174.30   $174.30  
  Purchase #4 $73.67   7.349%   $79.084   $79.08   $79.10   $79.10  
  Purchase #5 $43.70   7.563%   $47.005   $47.01   $47.00   $47.00  
  Purchase #6 $212.87   13.391%   $241.3754   $241.38   $241.40   $241.40  
  Purchase #7 $96.69   5.820%   $102.3174   $102.32   $102.30   $102.30  
  7 purchase totals = $941.05       $1,026.4884   $1,026.49   $1,026.50   $1,026.50